Construction Loan Draw Schedules and Interest Reserves: A Practitioner's Guide

Key Takeaways

Why Construction Loans Behave Differently

A construction loan is not a stabilized real estate loan with a different label. Its sizing constraints, draw mechanics, interest accrual, and risk profile are all materially different from permanent debt. Get the differences wrong and the deal looks underwriteable when it isn't, or the interest reserve ends up too small because it was sized off a shortcut that doesn't fit the draw schedule.

The structural differences come down to five facts. Construction loans are short-term: the term covers the construction period plus a lease-up period, often with extension options. They areinterest-only: principal isn't amortized during construction. They arefloating-rate, priced as a spread over SOFR (this article uses SOFR + 275–400 bps as an illustrative range for institutional sponsors). They are funded in draws against construction progress, not advanced in full at closing. And they are sized to loan-to-cost and projected debt yieldat stabilization, not to in-place NOI, because there is no in-place NOI during construction.

The article walks the five facts through one running deal: a $50M construction loan on a ground-up multifamily project in Phoenix, a 30-month draw schedule, priced at SOFR plus 325 bps. The interest reserve, the draw curve, and the circular reference between capitalized interest and total project cost get carried through end to end.

Anatomy of a Construction Draw Schedule

A construction loan funds in periodic draws against construction progress. The initial draw at closing typically covers land takedown plus pre-closing soft costs (design, permits, due diligence, financing fees), to the extent the sponsor's equity has not already paid for them. Subsequent monthly draws fund hard costs (materials, labor) plus continuing soft costs (architect, owner's rep, construction management fees, capitalized interest itself) against documented progress, usually an AIA G702/G703 contractor's application for payment, plus owner-controlled soft cost lines.

Three mechanics matter to the underwriter:

• Retainage. The owner withholds a share of each payment to the general contractor (and the GC withholds from its subcontractors) until the work is complete. Subject to state law, 10% is the rate most often used in the US, sometimes stepped down to 5% once the project is 50% complete (see thisoverview of retainage practice). Because the lender advances only what the owner actually pays, retainage keeps the loan balance lower during the build; the withheld amount then lands as a lump draw when it is released at substantial completion. On the worked example's $42M of hard cost, full 10% retainage is $4.2M. It is the contractor's money held back, not a sponsor outlay, but the model has to place the release in the right month.

• Lien waivers. Each draw requires lien waivers in the form state law requires: conditional waivers for the amount being paid with this draw and unconditional waivers for amounts paid through the prior draw. In Arizona, where the worked example sits, the statutory forms are inA.R.S. 33-1008; an unconditional waiver is enforceable once signed, even if the claimant has not been paid, so it belongs with payments that have already cleared. A missing waiver, or a supplier recording a mechanic's lien, can hold up a draw until the lien is released.

• Lender inspections. The lender engages an independent construction consultant (also called a project monitor or inspecting engineer) who reviews each draw request against the budget and schedule and certifies physical progress. The lender's draw approvals rely on that report, and the sponsor pays for it as a soft cost.

The S-Curve and Why Draw Timing Matters

Construction draws don't fund linearly. Cumulative cost typically follows an S-shape: a slow build during sitework and foundation; a steep climb during vertical construction (framing, MEP rough-in, envelope); and a taper through interior finishes and FF&E. The figure plots the worked example's loan draws over 30 months:

The curve matters because interest accrues only on the drawn balance, not on the loan commitment. A $50M loan drawn in a straight line to 100% by month 30 averages 50% outstanding. An S-curve that is symmetric about the midpoint also averages 50%: the slow start and the taper offset each other. What moves the average is timing. This schedule draws 42% of the loan in the first 12 months, so it averages 53%. A curve with heavier early draws averages more; a back-loaded curve averages less, and so does a loan where the sponsor's equity funds first, which PropertyMetrics noteslenders require in most cases. The 50% figure is a starting point to adjust, not an answer.

Interest Reserve Sizing, the Right Way

Two methods are in active use. The simple-average method takes an estimate of average outstanding balance, multiplies by rate and tenor:

For a $50M loan at 7.15% all-in over 30 months at 50% average outstanding, the simple-average formula gives: (0.50 × $50M × 0.0715) × (30 ÷ 12) = $4.47M. That is the quick estimate.

The draw-by-draw method projects the draws month by month (or in buckets), computes interest on the outstanding balance in each period, and sums. Applied to the worked example's schedule below, it gives $4.72M at a 53% average balance, so the shortcut understates the reserve by about $250K, or 5%.

The gap grows with front-loading. As an illustration, if draws were front-loaded enough that the loan averaged 62% outstanding, the reserve would be 0.62 × $50M × 0.0715 × (30 ÷ 12) = $5.54M. The gap to the shortcut is $1.07M: the true reserve is 24% higher than the shortcut, which means the shortcut understates it by 19%. That $1.07M is about 1.7% of total project cost (2.1% of the loan), and it has to come from somewhere when the reserve runs short.

Adventures in CRE's construction draw and interest calculation model is a pay-what-you-can monthly draw model that charges interest on previously accrued interest and, rather than using Excel's iterative calculation, solves for a target LTC with Goal Seek. PropertyMetrics's interest reserve walkthrough uses the simple-average formula, starts from 50% outstanding, says to adjust up for front-loaded draws and down for back-loaded ones, and notes that the result is an estimate only.

Worked Example: $50M Construction Loan

A 220-unit garden-style multifamily ground-up in Phoenix. Total project cost is $62.72M: $12M land, $42M hard costs, $4M soft costs (excluding capitalized interest), and a $4.72M interest reserve, which is the draw-by-draw interest from the schedule below. Construction debt is a $50M facility at SOFR + 325 bps (SOFR was 3.90% on October 6, 2026, per New York Fed SOFR data), giving an all-in cost of 7.15%. That is 79.7% LTC, at the top of this article's illustrative 65–80% range. The remaining $12.72M is sponsor equity, which funds the land at closing. The schedule runs 30 months from closing to the final draw.

The draw schedule, simplified to six-month buckets:

Total interest over the 30 months is approximately $4.72M, with an average outstanding balance of $26.4M / $50M = 53%. The buckets are smoothed totals of all loan advances, and each bucket's average balance is the prior cumulative balance plus half of that bucket's draw. This simplified schedule does not model retainage; a full model would show it as its own line: at 10% on $42M of hard cost, up to $4.2M is withheld during the build and released in the final draws, which shifts loan dollars later and lowers the average. For comparison, the 50% shortcut gives $4.47M, understating by $250K, or about 5%.

On an institutional underwriting, the budgeted reserve carries a cushion above the central estimate, and PropertyMetrics recommends erring on the high side. The cushion covers: (a) construction delays, which extend the period at peak balance; (b) SOFR moves during construction (if the loan has a rate cap, size the hedged balance at the cap strike plus spread; only unhedged exposure needs a stressed rate); and (c) hard-cost overruns that extend draws. As an illustrative assumption, a 15–20% cushion on the $4.72M central estimate ($0.7–0.9M) brings the budgeted reserve to roughly $5.4–5.7M. The sources-and-uses section below uses $5.5M for that case.

The Circular Reference Problem

Interest funded from the construction loan is itself a loan draw. Each month's interest increases the drawn balance, which increases the next month's interest. That is a circular reference: the reserve has to cover interest on the reserve.

There are two clean ways to handle it. The first is Excel's iterative calculation (File → Options → Formulas → Enable iterative calculation; the defaults are 100 iterations and a maximum change of 0.001). The model then finds the reserve that covers all interest, including the interest accrued on the reserve itself. The second avoids the circularity altogether: compute each month's interest on the prior month's balance, including previously accrued interest, and use Goal Seek or a short macro to size the loan to the target LTC. Adventures in CRE's model takes this second route.

A hard-coded reserve (say, $5.5M typed into sources and uses) removes the circularity but proves nothing on its own. It is acceptable only if the model checks it against the computed accrual and flags a shortfall. A reserve sized once at closing and never checked against the draw schedule is how burn-through surprises happen.

When the Reserve Burns Through

Construction loans assume the interest reserve covers all interest accrued during construction. When the reserve runs out before substantial completion, the lender has three options, none of which the sponsor wants to live through:

• Borrower-funded interest. The sponsor writes a check from equity each month to cover accrued interest until construction completes. This is the standard remedy in mid-stage burn-through; the sponsor's equity check effectively grows by the shortfall. On a 6-month delay past month 30 in the worked example, with the loan fully drawn at $50M, carry runs about $1.79M ($50M × 7.15% × 0.5), all of it unplanned equity unless the reserve cushion absorbs it. The illustrative 15–20% cushion ($0.7–0.9M) covers only about 40–53% of that.

• Reserve replenishment from contingency. If the budget has remaining hard-cost or soft-cost contingency, the lender may permit a rebalance, moving unused contingency into the interest reserve. This requires lender consent and amends the loan agreement. It works when contingency is intact; it is rarely available at the back of construction, when contingency has already been spent.

• Loan default / forbearance. When neither sponsor equity nor contingency is available, the lender enters workout. Practical resolutions include extending the maturity (with sponsor capital replenishment as a condition), partial deed-in-lieu, or in the worst case, foreclosure during construction.

Tying It to Sources and Uses

The interest reserve sits in sources and uses as a use of loan proceeds: the lender funds the reserve out of the construction loan itself. That ties reserve sizing to LTC. With the draw-by-draw reserve of $4.72M, total project cost is $62.72M and the $50M loan is 79.7% LTC, with $12.72M of sponsor equity. Had the budget carried the 50% shortcut ($4.47M), cost would show $62.47M and LTC 80.0%, and the $250K shortfall would surface later as sponsor equity. If the reserve carries the illustrative cushion to $5.5M, cost rises to $63.5M, LTC falls to 78.7%, and sponsor equity rises to $13.5M.

The same dynamic affects yield-on-cost and the development spread. Stabilized NOI of $4.5M at a 6.5% exit cap implies a $69.2M stabilized value. Against the $62.72M cost basis, yield-on-cost is 7.17% and the development spread (yield-on-cost at stabilization minus the exit cap) is 0.67%. At the $63.5M cost with the cushioned reserve, yield-on-cost is 7.09% and the spread is 0.59%. Small in isolation, but consequential as it compounds with other "small" cost overruns through the construction period.

The 2026 Rate Environment

Pricing inputs for this article, as of October 2026:

• SOFR 3.90% on October 6, 2026, published daily by the New York Fed
• Construction spreads (illustrative assumptions, not a survey): SOFR + 275–400 bps for institutional sponsors with stabilized rent comps; SOFR + 400–600 bps for first-time or less-capitalized sponsors
• All-in coupons at 3.90% SOFR: 6.65–7.90% across the institutional spread range; an illustrative debt-fund spread of SOFR + 600 bps gives about 9.9%
• Rate caps: floating-rate construction lenders may require one. Cap cost depends on the strike, term, notional, and rate volatility at purchase, so price it from a current quote and carry it as a project cost

The implication for interest reserves: SOFR averaged about 0.04% in the first quarter of 2021 (New York Fed data), so SOFR + 325 bps was about 3.3%. At 7.15%, the same $50M loan on the same 30-month schedule accrues about $4.72M of interest, versus about $2.2M at the early-2021 rate, roughly 2.2 times as much. Sponsors carrying reserve calculations from that period need to rerun them at current rates.

Six Mistakes Practitioners Make

• Using 50% average outstanding without checking the draw curve. Front-loaded draws push the average above 50%; back-loaded draws, or equity funding first, pull it down. The right number is the average of the actual draw schedule, not the convention.

• Treating SOFR as a static input. Construction loans are floating-rate. A sponsor who underwrote SOFR at 4.5% in early 2024 saw actual SOFR of about 5.3% from January through August 2024 (New York Fed data), roughly 80 bps above plan on every drawn dollar, before it fell back to about 4.3–4.4% in the first quarter of 2025. Model the rate cap as a real cost and the rate exposure as a real risk, and price the cap from a current quote.

• Treating retainage as sponsor cash, or ignoring it. Retainage is the contractor's money withheld until completion, not a sponsor outlay. 10% on $42M of hard cost is $4.2M that the loan does not advance during the build and then funds in a lump at release. Leave it out and the model draws too early (overstating interest) and misses the timing of the final draw and the final lien waivers needed to release it.

• Sizing the construction loan to in-place NOI. There is no in-place NOI during construction. Construction loans are sized to a combination of LTC (65–80% in this article's illustrative range) and projected stabilized debt yield (an illustrative 8.0% minimum). Anchoring LTV analyses against in-place NOI confuses the construction loan sizing with the permanent debt sizing.

• Underestimating soft cost burn-in. Soft costs (architect, owner's rep, financing fees, legal, permits, marketing, insurance) accrue continuously through construction and lease-up, not on the same S-curve as hard costs. Budget a separate soft-cost contingency rather than relying on the hard-cost contingency.

• Treating the construction loan as the takeout. The construction loan typically matures after substantial completion plus a lease-up period, often with extension options; the deal still needs a permanent loan or sale before that maturity. Sponsors who don't have a credible take-out plan in the underwriting fund themselves into a refinancing gap when the construction loan matures and permanent debt isn't available on the assumed terms. The 2026 vintage is more sensitive to this than 2018–2021 vintages because take-out debt costs more.

How to Model It in Excel

A practitioner-grade construction loan model has four tabs or sections:

• 1. Sources and uses. All-in project cost broken into land, hard costs, soft costs, capitalized interest, and contingency. Sources are equity, construction loan, and any subordinated debt or mezzanine. Reconciles to total cost. Capitalized interest is computed elsewhere and flows in.

• 2. Draw schedule. Month-by-month draws split by hard cost line, soft cost line, retainage withheld and released, and capitalized interest. Cumulative loan balance is the running sum. Average monthly balance is the input to the interest accrual.

• 3. Interest accrual. Monthly accrual = (prior-month balance + half of current-month draw) × (annual rate ÷ 12). Sum the monthly accruals to get total capitalized interest. The circular reference between the interest reserve (in sources & uses) and the capitalized interest (a draw line) is resolved with iterative calculation, or avoided by computing interest on the prior balance and sizing the loan with Goal Seek.

• 4. Sizing constraints. The loan is the lesser of (a) maximum LTC × total project cost, (b) stabilized NOI ÷ minimum debt yield (for example, $4.5M ÷ 8.0% = $56.25M), (c) maximum LTV × stabilized value (NOI ÷ exit cap), if the lender also tests LTV, and (d) any absolute commitment cap. In the worked example LTC binds: 80% × $62.72M is about $50.2M, against $56.25M by debt yield.

Do It in Apers

Related Articles

• Cap Rate Calculator and Formula: the exit-yield metric that drives takeout sizing.
• IRR Calculator and Formula for Real Estate: the development IRR these reserves feed into.
• Cash-on-Cash Return: Levered vs Unlevered: how the levered return changes during stabilization.
• IRR Sensitivity Analysis and Stress Testing: how to stress-test the development assumptions.

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