Private Activity Bonds and the 4% Credit: How Volume Cap Actually Works

Volume Cap: The Real Constraint Behind the 4% Credit

Tax-exempt private activity bonds are capped nationally under Internal Revenue Code Section 146. Each state gets its own annual volume cap -- an amount of tax-exempt bond authority it can allocate that year across every private-activity use the tax code recognizes, not housing alone. That list includes exempt facility bonds for airports and solid waste facilities, qualified student loan bonds, small-issue manufacturing bonds, and multifamily housing bonds, all drawing from the same statewide pool.

The cap itself is set by a per-capita formula with an inflation-adjusted floor for small states, both published annually by the IRS. For calendar year 2026, Revenue Procedure 2025-32 sets the amount at the greater of $135 per state resident or a $397,625,000 floor -- so a state's total bond authority for every private-activity use combined, housing included, is either its population multiplied by $135, or roughly $398 million, whichever is larger.

Multifamily housing bonds compete against every other private-activity use for a slice of that same statewide number. In states where bond demand runs high across all categories, the housing bond allocation itself becomes the practical constraint on how many 4% deals a state can close in a given year -- independent of how much 9% credit authority that same state has.

The Test That Actually Triggers the 4% Credit

Volume cap explains why bonds are scarce. It doesn't explain why bonds produce a 4% credit at all. That mechanism sits in Internal Revenue Code Section 42(h)(4)(B): if a specified share of a project's aggregate basis -- the buildings and the land under them -- is financed with tax-exempt bonds that count against volume cap, the entire eligible basis of the project qualifies for 4% credits without going through a state's separate competitive 9% allocation process.

For decades that specified share was 50%. A sponsor had to finance at least half the project's total basis with bonds to unlock 4% credits on 100% of eligible basis -- a real capital commitment, since every dollar of bond financing used to hit that 50% floor draws on the state's scarce, often-oversubscribed volume cap.

The One Big Beautiful Bill Act (OBBBA), signed July 4, 2025, cut that threshold from 50% to 25% of aggregate basis, for bonds issued and buildings placed in service after December 31, 2025. It's a permanent statutory change, not a temporary allowance.

Why Cutting the Test in Half Matters More Than It Sounds

The effect isn't just 'less bond financing required.' Because the 50% test had pushed housing bond demand close to the ceiling of available volume cap in a number of states -- industry commentary from Lument, an LIHTC-focused capital provider, has described the pre-2026 50% level as leaving housing bond demand 'nearly maxed out' and oversubscribed in roughly half the states -- a lower financed-by threshold means the same fixed pool of volume cap can now support meaningfully more total development cost in 4% deals than it could before, since each project only needs to draw a quarter of its basis from bonds rather than half.

There's a real tradeoff underneath that gain, worth naming rather than treating the change as a pure win. A sponsor that draws only the minimum 25% in tax-exempt bonds has to finance the remaining three-quarters of the capital stack some other way -- often with taxable debt, which the same industry commentary notes typically prices roughly half a percentage point higher than tax-exempt bonds. Freed-up volume cap doesn't automatically mean cheaper financing on any single deal; it means more deals can compete for the bond allocation that exists, and each sponsor still has to decide whether to draw the statutory minimum or a larger bond share to manage its own cost of capital.

How This Interacts with 2026's Bigger 9% Ceiling

This financed-by change landed in the same legislative package that permanently raised the annual 9% credit ceiling, and the two changes pull on the funding-gap math from different directions -- we've covered the 9% side of that story, including why a bigger ceiling hasn't made individual deals easier to close, in a separate look at the 2026 LIHTC funding gap. The short version that matters here: a site that would have been underwritten as a competitive 9% deal two years ago may pencil faster and more predictably as a 25%-test 4% bond deal now -- but only if that state's current bond volume and QAP scoring for bond deals actually support the swap, which is a state-specific, deal-specific question, not a blanket rule.

Where This Shows Up in a Deal

Testing whether a site is better underwritten as a 9% competitive deal or a 25%-test 4% bond deal means running both financing structures against the same site and comparing the results, rather than assuming the answer based on which credit type a sponsor has used before. EZFeasi's Subsidy Stack Optimizer models both credit-type paths side by side, so the comparison happens before a state's bond allocation or 9% round closes, not after. Book a demo to walk through how a specific site compares under each.