LIHTC Rent and Income Limits — AMI Calculations, Set-Aside Elections, and Pro Forma Impact

Key Takeaways

How AMI Sets the Ceiling

Every LIHTC deal starts with Area Median Income. AMI is the median income level for a metropolitan statistical area (MSA) or county. For LIHTC, HUD publishes Multifamily Tax Subsidy Project (MTSP) income limits each year, and LIHTC properties base their rents on those limits. AMI determines two things that govern every affordable housing pro forma: the maximum income a tenant can earn to qualify for a LIHTC unit under IRC Section 42(g), and the maximum rent a developer can charge for that unit.

HUD publishes MTSP income limits each spring: the FY2025 limits took effect April 1, 2025, and the FY2026 limits took effect May 1, 2026. The published figures are adjusted for household size, so the income limit for a three-person household differs from the limit for a four-person household. In the Figure 1 example below, the three-person limit is assumed to be 90% of the $85,000 four-person median ($76,500), an illustrative assumption. These adjustments matter because LIHTC rents are calculated from income limits, and income limits vary by household size.

For underwriting purposes, the critical figure is the income limit at the elected AMI percentage. A project electing the 60% AMI set-aside uses 60% of the area median income as its ceiling. A project using income averaging might have units at 30%, 40%, 50%, 60%, 70%, and 80% AMI. Each tier has a different income limit and a different maximum rent.

Maximum Rent Calculation

The maximum gross rent for a LIHTC unit is calculated through a specific chain that connects AMI to a dollar amount per unit per month. Every step introduces a variable that affects the final number.

Step 1: Determine the imputed household size

LIHTC uses the 1.5 persons per bedroom rule. The assumed household size for a unit is 1.5 times the number of bedrooms. For a studio or efficiency, the assumed household size is 1 person. This is an imputed assumption — the actual household size doesn't matter for rent calculation purposes.

Table 1 — Imputed household size by bedroom count. For fractional household sizes (1.5, 4.5), you interpolate between the published income limits for the two adjacent household sizes.

Step 2: Look up the income limit

Using the imputed household size and the elected AMI percentage, look up the corresponding income limit from HUD's published tables. For fractional household sizes, take the average of the two adjacent figures. For example, a 1-bedroom unit at 60% AMI uses the average of the 1-person and 2-person income limits at 60% AMI.

Step 3: Calculate gross rent

The maximum gross rent is 30% of the applicable income limit, divided by 12, as specified in IRC Section 42(g)(2). The 30% figure is statutory (IRC Section 42(g)(2)(A)); it parallels the 30%-of-income housing-cost benchmark in federal assisted-housing programs, which was originally 25% under the 1969 Brooke Amendment and was raised to 30% in 1981. Gross rent includes both the tenant-paid rent and the utility allowance.

Step 4: Subtract the utility allowance

The maximum tenant-paid rent — the amount that actually appears on the lease and flows into the revenue line of the pro forma — is gross rent minus the applicable utility allowance. This step is where many underwriting errors occur, because the utility allowance varies by unit type, heating fuel, and the method used to calculate it.

The Utility Allowance Deduction

The utility allowance is the single largest variable in the rent calculation after AMI itself. It represents the estimated monthly cost of tenant-paid utilities and is subtracted from gross rent to determine the maximum lease rent. A higher utility allowance means lower revenue for the project.

Treas. Reg. Section 1.42-10(b) sets which utility allowance applies. Rural Housing Service (RHS) assisted buildings use the RHS allowance, HUD-regulated buildings use the HUD allowance, and units with HUD-assisted tenants use the PHA allowance established for the Section 8 Existing Housing Program. For other buildings and tenants, the methods below apply. Where the choice is open, it can change net effective rent. As an illustrative assumption, the difference is $50-150 per unit per month.

• Public Housing Authority (PHA) schedule: The general rule when none of the higher-priority rules apply. The local PHA publishes utility allowances by unit type, bedroom count, and heating fuel. Once any of the estimates below is obtained, it replaces the PHA schedule for similar units in the building.
• Utility company estimate: Any interested party (a low-income tenant, the building owner, or the housing credit agency) may obtain a written estimate from the local utility company for a unit of similar size and construction.
• Agency estimate: The building owner may obtain a per-unit utility estimate from the housing credit agency with jurisdiction over the building, if the agency agrees to provide it.
• HUD Utility Schedule Model (HUSM): The building owner may calculate a utility estimate using HUD's Utility Schedule Model.
• Energy consumption model: The building owner may calculate estimates with an energy and water and sewage consumption model prepared by a properly licensed engineer or other qualified professional who is not related to the owner. The agency may approve or disapprove of the model.

For underwriting, the method matters because it directly affects the revenue line. A project with 100 two-bedroom units where the PHA schedule yields a $182/month allowance generates $74,400/year less in revenue than the same project using an energy consumption model that yields a hypothetical $120/month allowance (100 × ($182 – $120) × 12). That $74,400 annual difference compounds to about $1.1 million over a 15-year compliance period and can determine whether the deal is feasible.

Set-Aside Elections

Every LIHTC project must meet a minimum set-aside test under IRC Section 42(g)(1): a minimum percentage of units reserved for tenants at or below a specific income threshold. The developer elects one test on Form 8609 (line 10c), and the election is irrevocable once made (IRC Section 42(g)(1)). The project must meet the set-aside by the close of the first year of the credit period (IRC Section 42(g)(3)(A)). There are three options:

The 20/50 test

At least 20% of units must be rent-restricted and occupied by households with incomes at or below 50% of AMI. This election sets a lower unit count for compliance but limits rents to the 50% AMI level on those units, the lowest income tier available under the traditional set-aside structure.

The 40/60 test

At least 40% of units must be rent-restricted and occupied by households with incomes at or below 60% of AMI. It allows a larger share of units at the 60% AMI ceiling, which produces higher rents than the 50% threshold. A project in which every unit is income-restricted also satisfies 40/60, since all units already qualify. Projects located in New York City may not use the 40/60 test; they use the 25/60 test instead, under which 25% or more of the units must be rent-restricted and occupied by households at or below 60% of AMI (IRC Section 142(d)(6)).

Income averaging (the average income test)

At least 40% of units (25% in New York City) must be rent-restricted, and the average income limit across all restricted units must not exceed 60% of AMI. Individual units can be set at any 10-percentage-point increment between 20% and 80% AMI. This is the newest option, added by Division T, Section 103 of the Consolidated Appropriations Act, 2018 (P.L. 115-141) and codified as IRC Section 42(g)(1)(C), with IRS regulations at Treas. Reg. Section 1.42-19 (final regulations published in 2022, T.D. 9967, and final recordkeeping and reporting procedures published September 30, 2025).

Table 2. The three set-aside elections (New York City projects use a 25/60 test in place of 40/60). Income averaging offers the most flexibility by allowing some units at 80% AMI while maintaining a 60% average, but introduces compliance complexity.

Income Averaging

Income averaging fundamentally changes how developers think about unit mix and revenue. Instead of a flat ceiling where every unit is restricted to the same AMI level, developers can create a portfolio of AMI tiers across the project — as long as the weighted average does not exceed 60% AMI.

The practical effect: some units can be set at 80% AMI, producing higher rents than 60% units, while other units are set at 30% or 40% AMI, serving deeper affordability needs. The math must balance. For every unit at 80% AMI, there must be a corresponding unit (or units) at lower AMI levels to keep the average at or below 60%.

Worked example: 100-unit project with income averaging

Table 3. Income averaging unit mix. The weighted average (58%) is below the 60% ceiling. The 30 units at 80% AMI generate higher rents, while the 20 units at 30% AMI serve extremely low-income households.

Using the Figure 1 inputs ($85,000 four-person AMI, $182/month utility allowance), the 2-bedroom net rent is $966/month at 60% AMI and $1,348/month at 80% AMI, so the 30 units at 80% AMI generate $137,520/year more than the same units at 60% AMI, or about $2.1 million over a 15-year compliance period. The 20 units at 30% AMI and the 20 units at 50% AMI give up more than that: net rents of $392/month and $774/month are $183,840/year below the 60% rent on those 40 units. Netting the two effects, the 58% mix produces $46,320/year less than a flat 60% mix.

Compliance considerations

Income averaging adds designation and reporting steps that the traditional set-aside elections do not require. Under the average income test, each unit is designated at a specific AMI tier, and the project must keep the average of the designated limits at or below 60% AMI. A unit's designated limit is fixed (Treas. Reg. Section 1.42-19(c)(3)(iii)), and a household above a unit's designated limit at move-in does not satisfy that unit's limitation, although a continuing resident whose income later rises can remain qualified under Section 42(g)(2)(D). A limit can change only in the circumstances listed in Section 1.42-19(d)(1), such as agency-permitted changes or tenant movement within the project. If a unit loses low-income status or a limit changes, the owner can restore the 60% average by designating a market-rate unit or lowering the limits of other units (Section 1.42-19(d)(1)(v)). Failures to meet the recording and reporting procedures are treated as satisfied if the owner submits a correction to the agency within 180 days after discovery (Section 1.42-19(c)(4)).

AMI Trends and Deal Feasibility

AMI is not static. It moves with local economic conditions. These trends have direct underwriting implications because LIHTC maximum rents move with AMI: when AMI rises, maximum rents rise. When AMI stalls, limits stay flat and revenue projections built on historical growth rates will miss. The National Low Income Housing Coalition (NLIHC) "Out of Reach" report documents the gap between renter wages and the cost of rental housing.

A pro forma that projects rent growth of 2-3% annually implicitly assumes AMI growth at the same rate, since LIHTC rents are derived from AMI. But AMI growth is uneven across markets and across time. Under IRC Section 142(d)(2)(E)(i), as applied to LIHTC by Section 42(g)(4), the area median gross income used for a project cannot fall below the prior year's figure, and under Section 42(g)(2)(A) the income limitation cannot fall below the level that applied in the earliest period the building was in the project. A weak year therefore shows up as flat limits rather than lower ones. These swings directly affect whether a deal pencils.

The interaction between AMI trends and deal feasibility is particularly acute in markets where LIHTC rents are close to market rents. When AMI-derived maximum rents approach or exceed what the local market can absorb, the 30% of income constraint becomes a theoretical ceiling that tenants won't actually pay. In those markets, achievable rent — not maximum rent — governs the pro forma. The underwriter must use the lesser of the LIHTC maximum rent and the market rent achievable for comparable units in the submarket.

Common Mistakes

These are the errors that cause the most damage in LIHTC rent and income underwriting:

• Using 30% of AMI instead of 30% of the income limit. The income limit for a given household size at a given AMI percentage is not simply that percentage of AMI. HUD applies household size adjustments to the four-person median before multiplying by the AMI percentage. Using 30% of raw AMI instead of 30% of the published income limit produces the wrong rent for any unit whose imputed household size is not four persons.
• Forgetting to interpolate for fractional household sizes. A 1-bedroom unit assumes 1.5 persons. That means you average the 1-person and 2-person income limits. Using only the 1-person or only the 2-person limit will overstate or understate the maximum rent.
• Ignoring the utility allowance in preliminary feasibility. In early-stage underwriting, developers sometimes use gross rent as the revenue assumption. The utility allowance deduction reduces net rent; in this article's example, the $182 allowance is about 16% of the $1,148 gross rent. A deal that looks feasible at gross rent may not work at net rent.
• Relying on AMI growth to make the deal work. Test a 3% annual AMI growth assumption against flat limits. If the deal only works at 3% growth, it likely doesn't work: one flat year in the first five years of operations can create a cash flow shortfall that compounds through the compliance period.
• Assuming income averaging is always better. With a 58% average, income averaging produces less revenue than a flat 60% mix, as Figure 2 shows. Its value is deeper affordability on some units and access to households at 70-80% AMI, and it carries heavier designation and reporting requirements. Weigh those benefits against the added compliance cost.
• Using the wrong utility allowance method. The PHA schedule, HUSM, and energy consumption model can produce different allowances, and Treas. Reg. Section 1.42-10(b) determines which rules apply to a given building and tenant. Underwriting an allowance that the agency or the regulation does not support will require re-underwriting with a different allowance, which can change the deal's feasibility.

How to Model It

The rent and income calculation should be a dedicated tab in the LIHTC pro forma, not embedded in the operating revenue assumptions. Here's what it needs:

Income limit lookup

A reference table with HUD income limits for the project's MSA/county, by household size (1-8 persons) and AMI percentage (20%, 30%, 40%, 50%, 60%, 70%, 80%). This table should be updated annually when HUD publishes new limits. For forward projections, apply a growth rate to the base-year limits — but keep the growth rate assumption visible and adjustable.

Rent calculation matrix

For each unit type (studio through 4-bedroom), calculate: imputed household size → applicable income limit → gross rent (income limit × 30% ÷ 12) → utility allowance → maximum net rent. This should be done for each AMI tier if using income averaging.

Unit mix and revenue roll-up

The unit mix table should show: unit type, number of units, AMI designation, maximum net rent per unit, and total monthly/annual revenue. For income-averaged projects, include a weighted average AMI calculation that confirms compliance with the 60% average ceiling. The revenue roll-up feeds directly into the operating pro forma.

Sensitivity analysis

At minimum, test three scenarios: base case AMI growth, flat limits (the practical floor under IRC Sections 142(d)(2)(E) and 42(g)(2)(A)), and a market-rent haircut for units where the LIHTC maximum rent exceeds the rent the market will pay. Show how each scenario affects annual revenue, NOI, and DSCR.

Related Articles

This article is part of the LIHTC underwriting series. Each article goes deeper into a specific aspect of tax credit deal structuring:

• LIHTC 101: How the Program Works — The foundational overview of 4% vs 9% credits, credit calculations, and deal structure.
• The LIHTC Capital Stack — Soft debt, deferred developer fee, HOME funds, and gap financing.
• Acquisition/Rehab with 4% Bonds — Modeling existing property deals with rehabilitation credits.
• 4% LIHTC with Tax-Exempt Bonds — Bond deal mechanics, the 25% test, and how to size the bond tranche.
• LIHTC Investor Returns — Credit pricing mechanics, investor yield calculations, and pay-in schedule structuring.
• Year 15 Exit Strategies — Compliance period obligations, resyndication, and disposition options.