HAC: Hearing Aid Compatibility (FCC 20.19, C63.19)

Author Hugues Orgitello Last updated 14 June 2026 ~16 min read

FCC regulatory guide, US requirement

Hearing Aid Compatibility, or HAC, is the US requirement that obliges every mobile phone placed on the US market to demonstrate an acceptable level of radiofrequency interference and magnetic-field coupling with hearing aids worn by users. The framework is set by the FCC in 47 CFR 20.19, the measurement method by ANSI C63.19, and the scope expanded by the 2024 Report and Order, which phases in a 100 percent compatibility requirement between December 2026 and June 2028 and adds Bluetooth coupling alongside acoustic and telecoil coupling. This page covers the regulatory genesis from the Hearing Aid Compatibility Act of 1988 and its modernisation for mobile, the ANSI C63.19 metrology, the M and T ratings, the 2024 universal mandate and its deadlines, the distinction with SAR, and the most frequent pitfalls when preparing an FCC file for a product with a voice interface.

Regulatory genesis: from HAA 1988 to the 2024 universal mandate

The HAC requirement rests on a legislative and regulatory stack that every product manager must understand to anticipate evolution.

Section 710 of the Communications Act of 1934

The legal basis goes back to the Communications Act of 1934, codified in 47 USC. Section 710, added by the Hearing Aid Compatibility Act (HAA) of 1988 (Public Law 100-394), requires that all telephones manufactured or imported for use in the United States after August 1989 be compatible with hearing aids. The HAA then targeted wired telephones, in a context where T-coil coupling was the near-exclusive amplification path for hearing aid users.

2003-2007 modernisation for mobile

The FCC, through its 2003 Report and Order (FCC 03-168), extended the requirement to mobile phones, recognising that the historical exclusion of wireless handsets in the original HAA could no longer be justified in the era of widespread mobile use. The FCC adopted rating-based requirements for acoustic coupling and T-coil coupling (the ratings now known as M3/M4 and T3/T4) and imposed a progressive portfolio benchmark on operators and manufacturers: a given percentage of the portfolio had to be HAC. Successive amendments raised the portfolio benchmark, integrated new bands and services, and formalised periodic reporting.

2024 universal mandate, phased to 2026-2028

The Report and Order adopted by the FCC in 2024 carried out the major shift. The FCC found that coupling technologies were mature and widely deployed, that the per-model cost increment had become marginal, and that the historical portfolio benchmark left coverage gaps penalising hearing-impaired users. The universal mandate therefore requires that 100 percent of handset models offered to the US public be HAC, on a phased schedule written into 47 CFR 20.19(c): manufacturers from 14 December 2026, nationwide service providers from 14 June 2027, and non-nationwide service providers from 13 June 2028. Until those deadlines, at least 85 percent of the handset models in a portfolio must be hearing aid compatible. The rule also introduces Bluetooth coupling as an alternative to telecoil coupling, with a dedicated transition: from 13 December 2028, the Bluetooth coupling requirement may only be met with non-proprietary Bluetooth technology.

Timeline

Year	Regulatory act	Scope
1934	Communications Act	General framework for US telecommunications
1988	HAA, Public Law 100-394	Section 710 added, HAC for wired phones
2003	FCC Report and Order 03-168	Extension of HAC to mobile phones
2003-2017	Successive FCC amendments	M and T ratings, portfolio benchmarks, new bands and services
2024	FCC Report and Order, 100 percent mandate	Phased deadlines, Bluetooth coupling added, 85 percent benchmark meanwhile
2026	14 December 2026	Manufacturers: 100 percent of handset models HAC
2027-2028	14 June 2027 / 13 June 2028	Nationwide, then non-nationwide service providers at 100 percent

Structure of 47 CFR 20.19

The regulatory core fits within a specific paragraph of title 47 of the Code of Federal Regulations.

47 CFR 20.19(a), definitions and scope

Subparagraph (a) defines the terms: "hearing aid-compatible", "M rating", "T rating", "wireless handset", and bounds the scope. The scope covers "wireless handsets" understood as devices offering an interactive voice service on CMRS (Commercial Mobile Radio Service) services, which includes cellular phones, VoLTE phones, operator-subscription VoWiFi terminals, and certain two-way voice-interface IoT terminals.

47 CFR 20.19(b), technical requirements

Subparagraph (b) refers to ANSI C63.19 for measurement methodology and defines the technical requirements: acoustic coupling, telecoil coupling and Bluetooth coupling, with the M and T rating floors applicable under the 2007 and 2011 editions during the transition. Subparagraph (c) carries the deployment benchmarks: the 85 percent portfolio benchmark and the 100 percent deadlines of 14 December 2026 (manufacturers), 14 June 2027 (nationwide service providers) and 13 June 2028 (non-nationwide service providers).

Following subparagraphs, declaration and labelling regime

The following subparagraphs frame the regime of public declaration and periodic reporting to the FCC. The manufacturer must publish the M and T rating on the product sheet, the operator must display HAC availability in-store and online, and an annual aggregated report in CSV or PDF format is submitted to the FCC. Failure to comply with the declaration regime is a separate infringement from failure to meet the technical rating, and gives rise to financial penalties framed by 47 CFR 1.80.

See The FCC for the general framework of the US certification regime and FCC tests for the test chain required for a complete submission.

The ANSI C63.19 method

The ANSI C63.19 standard, drafted by the Accredited Standards Committee C63 of the IEEE, is the sole metrological reference cited in 47 CFR 20.19.

History and versions

Three editions are referenced in 47 CFR 20.19:

• ANSI C63.19-2007: historical edition, drafted in the GSM, CDMA and early 3G era. Referenced during the transition period for legacy ratings.
• ANSI C63.19-2011: intermediate edition extending the method to newer cellular technologies. With the 2007 edition, it defines the M and T rating system used during the transition.
• ANSI C63.19-2019: current edition. It underpins the coupling requirements of the 100 percent regime and is the reference for new submissions.

The FCC, in KDB 285076, publishes guidance explaining which edition of C63.19 is required according to the submission date and the embedded radio technology.

§ § §

Test bench and fixtures

A HAC campaign takes place in a laboratory equipped for near-field measurement in a controlled audio environment. Three elements characterise the bench:

• A semi-anechoic chamber or a certified quiet audio area, with residual background noise typically below 25 dB(A) to avoid polluting the T-coil coupling measurement.
• A handset positioning device in the Articulation Pole Position zone defined by the standard, that is, the position of a handset held to the ear in conversation. The fixture is typically a dummy head with a reference microphone and a magnetic-field sensor inserted in the zone corresponding to an ear canal fitted with a hearing aid.
• An audio magnetic-field sensor (typically a calibrated coil of the Bruel and Kjaer type or equivalent) and an RF electric-field probe for the M path, calibrated to the frequency and band being evaluated.

M path: RF interference at the hearing aid microphone

The M path evaluates the radiofrequency electric field radiated by the phone in the near zone of the microphone of an in-the-ear or behind-the-ear hearing aid. The measurement is taken with the handset placed in worst case (maximum power, antenna configured as in real use) and the E field recorded in V/m at the microphone position simulated in the fixture, on the operational bands of the handset. The rating is determined by the combination of the V/m value and the modulation category (RF noise category) of the signal, according to the tables of ANSI C63.19. The higher the M rating, the less RF interference the handset generates near the hearing aid.

T path: magnetic coupling with the T coil

The T path evaluates the magnetic coupling between the audio-frequency coil of the handset (typically a speaker drive or a dedicated coil in high-end phones) and the T coil (telecoil) built into most hearing aids. The measurement is taken in the audio band (300 Hz to 3.3 kHz typically), with a calibrated magnetic probe positioned in the zone corresponding to the T coil of the hearing aid. The rating depends on the useful audio magnetic field strength (conversation signal) and the absence of stray magnetic noise in the same band. The higher the T rating, the more efficient the coupling for the end user.

M3, M4, T3, T4 ratings: threshold table

The historical heart of HAC compliance lies in four ratings whose thresholds are published in the 2007 and 2011 editions of ANSI C63.19 and referenced in 47 CFR 20.19 for the transition period. Under the 2019 edition and the 100 percent regime, conformity is expressed as meeting the acoustic coupling requirement plus either the telecoil or the Bluetooth coupling requirement.

Rating	Path	Quantity evaluated	ANSI C63.19 threshold	Practical reading
M3	Acoustic (RF at microphone)	RF E field in near zone	Acceptable level, category 3	Rating floor to count as HAC
M4	Acoustic (RF at microphone)	RF E field in near zone	Stricter level, category 4	Recommended for premium
T3	T-coil (magnetic field)	Useful audio strength vs noise	Acceptable level, category 3	Rating floor to count as HAC
T4	T-coil (magnetic field)	Useful audio strength vs noise	Stricter level, category 4	Recommended for premium

The precise numerical thresholds (V/m for M, dB(A/m) for T, and signal-to-noise quality coefficients for both paths) are listed in the tables of the ANSI C63.19 edition used for the submission. The standard is under IEEE copyright and requires purchase for access to the exact figures. The reader should take the levels expressed here in words as reflecting the structure of the tables without reproducing their values: any measurement report must cite the thresholds of the exact C63.19 version used.

Why M4/T4 rather than M3/T3

M3 and T3 are the rating floors for a handset to count as hearing aid compatible under the 2007 and 2011 editions. Several manufacturers nonetheless aim for M4 and T4 for two reasons. The first is marketing: a phone rated M4/T4 is perceived as premium by hearing-impaired users and their prescribing ENT specialists. The second is defensive: the extra margin absorbs manufacturing drift and last-minute adjustments (antenna change, band addition), avoiding a return to the laboratory at pre-production stage.

HAC vs SAR: two separate requirements

The HAC / SAR confusion is the most common cause of planning errors in product preparation. The two requirements coexist in an FCC file for a phone, but they cover different physical quantities and health objectives.

Criterion	SAR (47 CFR 2.1093)	HAC (47 CFR 20.19)
Health objective	Limit RF absorption by tissue	Ensure phone usage with a hearing aid
Measured quantity	SAR in W/kg, 1 g average	RF E field in V/m and magnetic field in dB(A/m)
Phantom	SAM head or flat body phantom	Dummy head with built-in T coil
Measurement band	100 kHz to 6 GHz (carrier), plus mmWave in density	Cellular carrier + audio band (300 Hz to 3.3 kHz)
Methodological standard	IEC 62209 (transposed EN)	ANSI C63.19
Validation limit	1.6 W/kg over 1 g (US)	M3+/T3+ ratings, or coupling requirements of the 2019 edition
Coupling type studied	Volumetric absorption in tissue	RF interference + audio magnetic coupling

For SAR context, see SAR procedures (IEC 62209, EN 50360). For the terminology definitions used here, see the Glossary.

Concrete case: a product can be SAR-OK and HAC-KO

A smartphone with its main antenna housed at the top of the device, optimised for an acceptable 1 g averaged SAR, can nonetheless generate high field density in the immediate vicinity of the earpiece speaker, the exact zone of the HAC M-path fixture. Conversely, a very RF-economical phone (and therefore HAC-friendly) may show a SAR limited by poor spatial distribution of the field in the phantom. The two campaigns are therefore independent in practice, even if they are scheduled over the same period to share the bench and the instrumentation.

Geographic coverage: is HAC required outside the USA?

HAC is primarily a US topic. The regulatory map is uneven.

Region	Equivalent HAC requirement	Reference
United States	Mandatory, universal mandate	47 CFR 20.19 + ANSI C63.19
European Union	No direct requirement	RED 2014/53/EU article 3.1(a) health, 3.1(b) EMC, with no dedicated HAC threshold
Canada	Recommended / aligned with FCC	ISED SP-Std-503, derived from ANSI C63.19
Australia	Dedicated reference	AS/CA S040, requirements close to the FCC model
United Kingdom	No direct requirement post-Brexit	UK PSTI framework and UK Radio Equipment Regulations with no dedicated HAC
Japan	Indirect reference via MIC	No universal mandate
South Korea	Indirect reference via KCC	No universal mandate
Brazil	No specific ANATEL requirement	May follow global manufacturer practice

For a global manufacturer, the common practice is to design the US version HAC-compliant and to deploy it worldwide, thereby avoiding hardware fragmentation. See The RED for the general European framework and RED tests for radio, health and EMC testing.

Special cases and exclusions

47 CFR 20.19(b) and the associated KDBs describe several special cases and partial exclusions.

WLAN-only and VoWiFi devices

Handsets offering operator-grade voice over Wi-Fi alongside a mobile service (operator-subscription VoWiFi, voice applications integrated into the service of an MVNO) are treated within the HAC framework. A pure Wi-Fi terminal without an associated CMRS function remains out of scope as long as it does not offer a two-way service-quality telephony service. The boundary is not always clear-cut, and the FCC rules case by case through KDBs and ruling letters.

Vehicle-embedded phones (eCall, ambient calling)

Cellular phones integrated into a vehicle, dedicated to emergency calls (eCall for the EU, functional equivalent for the US market) or to user comfort (automotive Wi-Fi hotspot with voice function), benefit from partial exclusions. The derogation is grounded in the fact that the device is not held to the ear in normal use but used via the vehicle audio system. Technical documentation must demonstrate the usage mode and the absence of an associated portable handset.

Two-way satellite phones

47 CFR 20.19 frames its scope around handsets used with terrestrial mobile service. The regulatory treatment of two-way satellite handsets and of emerging direct-to-cell satellite services is therefore less clear-cut and has evolved with FCC practice: a manufacturer of a satellite-capable handset should confirm the applicable HAC obligations with a TCB or against the current FCC guidance rather than assume an exemption or an obligation.

Articulation with ANSI C63.20 (wireless headsets)

ANSI C63.20-2019, published in parallel with C63.19-2019, addresses HAC for wireless audio accessories (Bluetooth headsets, in-ear earbuds, circumaural headphones), that is, devices that interact acoustically or magnetically with a hearing aid without constituting a telephony handset in the strict sense.

For a smartphone shipped with branded Bluetooth earbuds (which has become standard since 2020), the FCC TCB typically requests:

• An ANSI C63.19 campaign for the handset (smartphone).
• An ANSI C63.20 campaign for the audio accessories shipped in the catalogue.
• A joint declaration in the product file.

ANSI C63.20 is not formally mandated by 47 CFR 20.19, but TCB practice is to require it to close a complete file for a product with Bluetooth accessories. For accessories not shipped in a bundle (purchased separately), HAC responsibility falls back on the accessory manufacturer alone.

Real-Ear Measurement and volume control

Two complementary functional requirements were added to the HAC regime through successive amendments.

Volume control consistent with HAC

47 CFR 20.19 requires that the handset volume-control range allow a hearing aid user to obtain a comfortable audio level without saturating or going below the audibility threshold, by reference to the dedicated volume-control standard cited in the rule. A handset that does not offer a sufficient volume range may be HAC-compliant on the M and T paths but non-compliant on the volume-control path, which invalidates the file.

Real-Ear Measurement (REM)

Real-Ear Measurement is the audiological reference technique used by ENT specialists to verify the actual adequacy of hearing-aid amplification to the wearer's ear canal. Although REM itself is not a regulatory obligation imposed on the phone manufacturer, ANSI C63.19 cites REM as the physiological reference of the evaluation zone: the HAC fixture is designed to reproduce the conditions under which an audiologist would verify the hearing aid in REM. Metrological traceability of the HAC result back to REM is considered a strength of the product file, without being mandatory.

Classic pitfalls in HAC preparation

First-pass rejections at TCB on the HAC part come from four recurring causes.

1. Late discovery of the HAC requirement. The product team sets the specification without explicitly including HAC, assuming it is covered by SAR or by general EMC. The laboratory discovers the requirement at pre-submission stage, and a second campaign must be ordered (two weeks, 8,000 to 15,000 EUR) with possibly an antenna re-spin if the target rating is not reached. The rule is to record HAC M3+ T3+ in the specification from concept stage and to open a dedicated budget for the HAC laboratory.

2. Omission of the telecoil or Bluetooth coupling path. Under the portfolio benchmark regime, many manufacturers settled for acoustic coupling without implementing a dedicated audio T coil. From 14 December 2026, every new model must meet acoustic coupling plus either telecoil or Bluetooth coupling, and from 13 December 2028 the Bluetooth route must use non-proprietary technology. A product that has planned neither a drive circuit for the T coil nor a compliant Bluetooth coupling path at the electronic design stage ends up having to add a component at a late phase, which impacts the BOM, PCB routing and enclosure. The rule is to choose and design the second coupling path in the initial schematic for US-targeted phones.

3. Confusion between SAR compliance and HAC compliance. The certification lead assumes that the SAR report covers the HAC requirement. This is never the case: these are two separate campaigns, two reports, two sets of instrumentation. The rule is to schedule two parallel campaigns at the same laboratory if possible, sharing the bench but with two sets of fixtures and two sets of probes. For an overview of the associated FCC tests, see FCC tests.

4. Wrong product classification. A voice-interface IoT terminal (for example a smart speaker capable of placing a phone call via VoIP integrated into an operator service) can fall within the HAC scope without the product team anticipating it. The rule is to verify the CMRS classification of the product with an FCC consultant or directly with a TCB at concept stage, before design freeze.

See FCC pitfalls for the general pitfalls of a US certification file and FCC procedure for the full submission chain.

Schedule and cost of a HAC campaign

For a go-to-market budget, here are the orders of magnitude observed in an ISO/IEC 17025 accredited laboratory recognised by the FCC for HAC testing.

Product type	Configurations to evaluate	Campaign duration	Indicative cost
Single-band LTE mobile phone	8 to 15	4 to 6 days	6,000 to 10,000 EUR
Multi-band 4G + sub-6 GHz 5G NR smartphone	20 to 40	1.5 to 2.5 weeks	12,000 to 22,000 EUR
Smartphone 4G + 5G FR1 + Wi-Fi 6E + BLE	40 to 70	2.5 to 4 weeks	20,000 to 35,000 EUR
Two-way satellite handset	10 to 20	1 to 2 weeks	10,000 to 18,000 EUR
Vehicle-embedded phone eCall + voice	5 to 12	1 week	7,000 to 12,000 EUR

The cost depends mainly on the number of operational bands and the number of configurations to evaluate (low, middle, high channel on each band, plus multi-radio configurations). A product with active beamforming (5G FR1 with synchronous multi-antennas) requires angular scanning that can multiply campaign duration by 1.5 to 2. See Certification costs for the overall budget framework of a product certification.

Key takeaways

• HAC is a US-specific requirement, with no direct EU equivalent, framed by 47 CFR 20.19 and the ANSI C63.19 methodology.
• The 2024 Report and Order phases in 100 percent compliance: manufacturers from 14 December 2026, nationwide service providers from 14 June 2027, non-nationwide providers from 13 June 2028, with an 85 percent portfolio benchmark until then.
• Coupling paths combine. A compliant handset meets the acoustic coupling requirement plus either the telecoil or the Bluetooth coupling requirement; the M and T ratings come from the 2007 and 2011 ANSI editions used during the transition.
• HAC and SAR are independent. A product may be SAR-compliant and fail HAC, or the reverse, because the physical quantities, phantoms and measured bands differ.
• ANSI C63.19-2019 is the current edition; 47 CFR 20.19 also references the 2007 and 2011 editions. ANSI C63.20-2019 addresses HAC for wireless audio accessories.
• The main pitfall is the late discovery of the requirement during the product cycle, leading to an antenna re-spin or to a costly second laboratory campaign.

For practical application on the US side, see FCC tests and FCC procedure. For the SAR context with which HAC is coordinated, see SAR procedures (IEC 62209, EN 50360). For the definition of the terms M, T, HAC, see the Glossary.

See also

• EN 50332: acoustic safety of music players + headphones
• AT&T NAF / NAFI: carrier homologation, cellular IoT
• Verizon OPC: carrier homologation after PTCRB
• NTT DoCoMo, KDDI, SoftBank, Rakuten: Japan cellular
• CPSIA and ASTM F963: toy safety in the United States
• EASA C0 to C6: UAS drone classes and ID labelling
• ISO 10218 and ISO/TS 15066: robotics and cobot safety

Working on antenna specification and design of a telephony handset with HAC rating M3+/T3+ and target SAR for a real product? AESTECHNO can audit your design and certification plan. Get in touch →

Sources & references

1. FCC, Hearing Aid Compatibility for Wireless Telephones , Federal Communications Commission www.fcc.gov/consumers/guides/hearing-aid-compatibility-wireless-telephones
2. 47 CFR 20.19, Hearing aid-compatible mobile handsets , eCFR / FCC www.ecfr.gov/current/title-47/chapter-I/subchapter-B/part-20/section-20.19
3. ANSI C63.19-2019, Methods of Measurement of Compatibility between Wireless Communications Devices and Hearing Aids , IEEE / ANSI ASC C63 standards.ieee.org/ieee/c63.19/4748/
4. Section 710 of the Communications Act of 1934 (HAA 1988, codified 47 USC 610) , Cornell Legal Information Institute www.law.cornell.edu/uscode/text/47/610
5. ANSI C63.20-2019, Methods of Measurement for Wireless Devices Supporting Hearing-Aid Coupling , IEEE / ANSI ASC C63 standards.ieee.org/ieee/c63.20/10717/