Construction Interest Reserves: How to Size One Before a Lender Does It for You

Most builders know their hard costs to the dollar. Fewer have a precise answer to a quieter question: how will the interest get paid while the project produces no income?

On a construction or bridge loan, the usual answer is an interest reserve. It is a line item inside the loan budget that pays the monthly interest until the property sells, refinances, or starts producing enough income to carry itself. Size it well and the project funds itself through completion. Size it badly and you are writing checks from personal liquidity in the last three months of the build, which is exactly when cash is tightest.

The margin for error is narrower than it was a few years ago. The Texas Real Estate Research Center's Spring 2026 housing report, drawing on Texas REALTORS data, shows the share of new-home sales priced below $300,000 fell to the low 20% range by fall 2022 and climbed back to roughly a third in 2025, while the share above $500,000 fell from a record 25% to 26% in fall 2022 to below 20% by 2025. The new-home mix has shifted back toward lower price points, and at lower price points every month of carry takes a larger share of the profit.

How an Interest Reserve Actually Works

An interest reserve is not cash sitting in an account. It is part of the loan commitment, set aside in the budget and drawn monthly to pay interest as it comes due.

Three features matter:

• Interest is charged on what has been drawn, not on the full commitment. Early in a build, the outstanding balance is small. It grows with each draw, so the monthly interest grows too. The heaviest interest months come at the end, not the beginning.
• The reserve itself is borrowed money. Each interest payment funded from the reserve increases the loan balance, and that added balance also accrues interest.
• The reserve counts toward total project cost. If a lender caps the loan at a percentage of cost, a larger reserve uses some of that capacity. That is a trade-off to see clearly, not a reason to under-size it.

When the reserve runs out before the project exits, the borrower pays interest out of pocket. A missed interest payment is generally a default under the loan documents, however well construction is going.

Sizing the Reserve Without Guessing

The cleanest method is to build it from the draw schedule rather than from a rule of thumb.

1. Lay out the draw schedule by month

Start with your construction budget and your realistic build timeline. Estimate how much will be drawn in each month: land or lot payoff at closing if it is financed, then site work, foundation, framing, mechanicals, finishes, and closeout. Lenders will release funds against inspected progress, so tie each month to work that can actually be verified.

2. Calculate interest on the running balance

For each month, take the cumulative amount drawn, including prior interest funded from the reserve, and apply the note rate from your term sheet. Sum those monthly figures through completion.

3. Add the exit period

This is where most reserves come up short. Completion is not the exit. A for-sale home needs time to list, go under contract, and close. A rental or commercial project needs time to lease up and qualify for a takeout loan. Add the months you realistically expect between completion and payoff, at the full outstanding balance, because the balance is at its peak during that window.

4. Add a cushion for delay

Inspections slip. Utilities connect late. Weather costs a few weeks. Price the reserve with a delay scenario, not just the base case, and decide in advance how you would fund interest if the delay runs past the cushion.

What Lenders Look at When They Review Your Reserve

Private lenders read the reserve as a signal of how well the sponsor understands the project. A reserve that only covers the build period, with nothing for sale or lease-up, tells a lender the exit has not been thought through.

Expect questions about:

• Timeline support. How long have comparable projects taken to build and sell or lease in this submarket, and what is your own track record?
• Exit evidence. Comparable sales or rents, a builder pre-sale or listing plan, or a takeout lender's preliminary interest.
• Liquidity outside the loan. Lenders want to see that you could carry the interest for a period if the reserve runs short.
• Extension terms. If the loan allows extensions, know the fees and conditions now. An extension is not a substitute for an adequate reserve, but it should be priced into the downside case.

For value-add bridge loans, the same logic applies. The reserve should carry the property through renovation and stabilization, with the business plan showing when in-place income is expected to cover debt service.

Put the Numbers on Paper Before You Apply

Before you request terms on your next build or bridge project, put three things on one page: the monthly draw schedule, the calculated interest through exit, and a delay case with your plan for covering it. A file built that way answers the questions a lender would otherwise price as risk.

PLG Capital structures and places construction, land, and bridge financing for Texas builders and investors through a network of private lenders. If you want a second set of eyes on your budget and reserve before you go to market, send us the project and we will tell you what the file needs and where it is likely to fit.