Why Construction Loan Interest Works Differently

Understanding how interest accrues on a construction loan is one of the most important things a builder can get right before committing to a project. Unlike a conventional mortgage where you borrow the full amount at closing and pay interest on the entire balance from day one, a construction loan disburses funds in draws over the course of the build. You only pay interest on the amount that has actually been funded.

This means your interest costs start low in the early months of the project when only the initial draws have been funded, and increase as more draws are released and your outstanding balance grows. By the final months of the project, you are paying interest on the full loan amount. The calculator above models this precisely so you can see your actual month-by-month interest obligation rather than estimating from the full loan balance.

For a typical 12-month construction loan with even monthly draws, the total interest cost works out to approximately 55% to 60% of what you would pay if the full loan amount had been outstanding for the entire term. That is a meaningful difference on a $1.5 million loan, and it is one of the reasons construction loan interest is often less expensive in practice than it appears on the term sheet.

How to Use This Calculator to Evaluate Your Deal

The construction loan interest calculator is most useful when you use it as part of a complete deal analysis, not in isolation. Here is how experienced builders integrate interest cost into their underwriting.

Start with your total loan amount and the rate you have been quoted. Enter the term that matches your realistic construction timeline, not the optimistic one. Builders consistently underestimate how long projects take. If you think the project will take ten months, model twelve. The extra two months of interest cost will either confirm that the deal works with cushion or reveal that your margin is thinner than you thought.

Model the draw schedule that reflects how your specific project will actually be funded. A ground-up new construction project typically has large early draws for site work and foundation, a substantial framing draw, and then a series of smaller draws through the finish phase. Front-loading your model gives you a more conservative interest estimate, which is always the right approach when you are underwriting a deal.

Add the total financing cost from the calculator to your hard construction costs, soft costs, land acquisition cost, and selling costs to get your true all-in number. Then compare that to your projected exit price. The spread between your all-in cost and your exit is your profit. If that spread is not large enough to absorb a 10% miss on either side, the deal needs to be renegotiated or passed on.

What Private Construction Loan Interest Rates Actually Look Like in 2026

Private construction loan interest rates in Massachusetts and across New England currently run between 10% and 12% for experienced borrowers with strong track records and well-underwritten deals. Rates at the lower end of that range are available to borrowers with multiple completed projects, clean credit, and deals that have meaningful equity cushion relative to the projected exit price. Rates at the higher end reflect higher loan-to-value ratios, borrowers with limited track records, or deals in markets with less predictable exit values.

In addition to the interest rate, private construction loans typically carry an origination fee of 1.5% to 3% of the loan amount, paid at closing. At Mayflower Venture Partners, our origination fees are in that range depending on the deal. The origination fee is a one-time cost that should be factored into your total financing cost analysis alongside the monthly interest obligation.

The total financing cost on a well-structured private construction loan for a $1.5 million project at 10.99% over 12 months with even draws is approximately $90,000 to $100,000 in interest, plus the origination fee. For a project that generates $300,000 or more in gross profit on a $2 million exit, that financing cost represents an excellent use of capital.

We provide new construction loans throughout Massachusetts and across New England. If you want to talk through the financing cost on a specific deal you are evaluating, call us. We will walk through the numbers with you and give you a straight answer on whether we can finance it and on what terms.