Capital Stack Builder.

How the builder works

This is a working sources & uses model. Uses is your total development cost. Sources are computed from inputs you control: LIHTC equity = eligible basis × boost × applicable fraction × rate × 10 × credit price; permanent debt = stabilized NOI ÷ DSCR ÷ the annual mortgage constant (including MIP). Soft debt and deferred developer fee are sources you enter; the leftover is the funding gap (or surplus). Nothing is hardcoded — change any assumption and the stack responds. It loads pre-filled with illustrative defaults (an FHA 221(d)(4)-style loan) so you can see a full stack immediately. It is still a feasibility screen, not a substitute for your syndicator's underwriting.

What you control

Nothing material is hardcoded. Every driver below is an input you set, and the stack recomputes live:

• LIHTC equity. Eligible basis (enter it as a % of TDC or override with a dollar figure — or build it line-by-line in the Eligible Basis Calculator and hand it over), the 130% boost, applicable fraction, credit rate, and credit price are all editable. Equity = eligible basis × boost × fraction × rate × 10 × price. On an acquisition/rehab deal, enter the existing-building acquisition basis (excl. land) separately: it is credited at 4% (the §42(b)(3) floor) and never boosted, and the Eligible Basis Calculator hands it over automatically.
• Permanent debt. Built from a transparent NOI: gross potential rent − vacancy + other income − operating expenses − replacement reserves. Debt = NOI ÷ your DSCR ÷ the annual mortgage constant, where the constant is computed from your interest rate and amortization with MIP added on (the FHA method). Set MIP to 0 for conventional/GSE debt.
• Other sources. Soft debt (HOME, HTF, state, AHP) and deferred developer fee are sources you enter. The residual is the funding gap (or surplus).
• 4% + bond deals. Switching to 4% sets the credit rate to the 4% floor and shows the tax-exempt bond as a memo only — bonds finance construction and are taken out by the permanent loan at conversion, so they are not double-counted as a permanent source.
• Loads with illustrative defaults (100 units, $125k/unit TDC, 75% basis, $0.90 price; $700 rent, 7% vacancy, $4,500 opex, $500 reserves, 1.2× DSCR, 4.5% / 40-yr, 0.25% MIP — the flat FHA multifamily annual MIP for applications on/after Oct 1, 2025, per HUD's Sept. 23, 2025 notice, 90 FR 45789). For conventional/GSE debt set MIP to 0 and amortization to your lender's term (often 30 years); for FHA 223(f) the term is capped at 35 years.

What this builder doesn't do

• It doesn't build your uses. Total development cost is a single input. For the cost-side build-up (hard cost, contingency, GC, soft costs, developer fee) use your development budget; for the eligible-basis portion use the Eligible Basis Calculator.
• No state HFA specifics. Bond-cap rules, gap-subsidy programs, and QAP sizing constraints vary by state and are not modeled. See the relevant state HFA page.
• It doesn't quote rates or pricing. Interest rate, MIP, DSCR, and credit price are your inputs — the defaults are illustrative, not quotes. Confirm execution (FHA 221(d)(4)/223(f) vs GSE) with your lender and pricing with your syndicator.
• No income-averaging or unit-mix detail. The applicable fraction is a single input; an income-averaged project has a unit-by-unit designation that affects basis and rents.
• Not an underwriting model. It is a feasibility screen — a full pro forma with a 15-year cash flow, lease-up, and exit comes from your syndicator.

What to do with the output

Read the gap. A small gap (<10% of TDC) is usually closable with normal state/local soft money and deferred fee. A large gap (>25%) means the deal needs deeper subsidy, lower cost, or higher NOI — tune the inputs to see what closes it. A surplus means you can reduce hard debt (improving coverage) or equity. For deals that pencil, the next step is your syndicator's full underwriting — not this tool.

Sources

• IRC § 42 (LIHTC) — applicable percentages, eligible basis, qualified basis, basis boost
• IRC § 42(h)(4)(B) — bond financed-by test: two alternative pathways for buildings placed in service in taxable years beginning after Dec 31, 2025 — (A) ≥50% of aggregate basis (building + land) financed by tax-exempt bonds (any issue date), or (B) ≥25% of aggregate basis bond-financed AND ≥5% of aggregate basis financed by bonds issued after Dec 31, 2025 (P.L. 119-21 §70422)
• IRC § 42(d)(5)(A) — federal grants excluded from eligible basis (grant-financed costs are not counted)
• P.L. 119-21, One Big Beautiful Bill Act, enacted July 4, 2025
• HUD, “Changes in Mortgage Insurance Premiums Applicable to FHA Multifamily Insurance Programs,” 90 FR 45789 (Sept. 23, 2025) — flat 0.25% annual MIP for applications submitted or amended on/after Oct 1, 2025
• HUD MAP Guide (4430.G) — max term 40 years for 221(d)(4) new construction/substantial rehab; 35 years (or 75% of remaining economic life) for 223(f)

Disclaimer

The Capital Stack Builder is a feasibility-stage screening tool with simplified inputs and assumptions. It is not an underwriting model and does not substitute for a full pro-forma from your accountant or syndicator. Equity pricing, debt rates, opex ratios, and many other inputs vary widely by market and deal. Always confirm modeled numbers with a qualified professional before relying on them for a transaction. This is educational content and is not legal, tax, or financial advice.