Construction Loan Calculator

How the construction loan calculator works

A construction loan has two lives, and this calculator models both. During the construction phase, money is released in stages as the build progresses, and you pay interest only on the amount drawn so far. Because the balance climbs from near zero to the full loan over the build, the payment starts small and grows, and the average balance is roughly half the loan — so the tool estimates total construction interest as the loan times the construction rate over the period, halved. It also shows the peak interest‑only payment you would reach when the loan is fully drawn.

When the home is finished, a construction‑to‑permanent loan converts to an ordinary mortgage. The calculator amortizes the full loan at your permanent rate and term to give the fixed monthly payment you will make for the life of the mortgage, plus the total interest over that period. Seeing the two phases side by side helps you budget for the build — when you may also be paying rent or another mortgage — and for life afterward. If you are buying the lot separately, pair this with the land loan calculator.

Budget for the build, not just the mortgage

The trap with construction financing is focusing only on the eventual mortgage payment and forgetting the build itself. During construction you carry the interest cost that grows as draws are released, and you often carry it on top of your current rent or mortgage, since you have nowhere to live yet. Add the near‑universal reality of construction — overruns and delays — and the construction phase can strain cash flow more than the permanent payment ever will. Build a contingency into your budget and confirm how your lender handles a project that runs long.

One loan or two?

A construction‑to‑permanent loan is usually the cleaner path: you apply and close once, and the loan rolls into a mortgage automatically when the home is done, locking in your terms up front. The alternative — a standalone construction loan followed by a separate mortgage — means qualifying and paying closing costs twice, and risks a higher rate if the market moves against you before the second loan. Unless you have a specific reason to separate them, the single‑close option saves money and uncertainty.

One-time-close vs two-close construction loans

How many times you go to closing is one of the biggest choices in construction financing. A one-time-close loan — the construction-to-permanent loan this calculator models — wraps the build and the final mortgage into a single loan with one application, one closing and one rate lock. You qualify once, and when the home is finished the loan simply converts to a regular mortgage. A two-close structure uses a short-term construction loan first, then a separate mortgage to pay it off when the home is done. That means qualifying and closing twice, paying two sets of closing costs, and — the real danger — facing whatever mortgage rates exist at the end of the build rather than the rate you locked at the start. Most borrowers prefer one-time-close for the simplicity and rate certainty; two-close mainly survives where a builder or program requires it.

Estimate only — not a loan offer or financial advice. Construction interest depends on the actual draw schedule and timeline, so real figures vary. Confirm terms, rates and draw rules with your lender.

How to use it & key terms

Enter the total project cost, your down payment, the construction rate and build length, and the permanent rate and term, then press Calculate to see the construction interest and the permanent payment.

How lenders approve and release the money

A construction loan is underwritten against a house that does not exist yet, which is why the approval process asks for more than a standard mortgage does. Because there is no finished home to appraise, the lender relies on an as-completed appraisal — an estimate of what the property will be worth once built — based on your plans and specifications. Expect to provide detailed drawings, a realistic budget, and usually a fixed-price contract with a licensed builder the lender is willing to approve. Many lenders also want to see a contingency reserve set aside for surprises and often ask for a larger down payment than a purchase mortgage, since a half-built project is difficult to sell if anything goes wrong.

Once the build begins, the money is not handed over in a lump sum. It is released in stages called draws, each tied to a milestone — foundation poured, framing complete, roof on, and so on. Before releasing a draw, the lender typically sends an inspector or appraiser to confirm that the work claimed has actually been done, and only then advances that portion of the loan. Some lenders keep a holdback, a small percentage of each draw retained until the project passes its final inspection, to make sure the last stretch of work is finished properly.

This staged approach is what protects both sides. You only pay interest on the money actually drawn, so the carrying cost rises gradually rather than all at once, and the lender never has more cash exposed than there is completed value to back it. It also means delays and disputes over whether a stage is truly finished can hold up funding, so keeping the draw schedule, the builder, and the inspections moving in step matters as much to your cash flow as the interest rate.

The build ends with a final inspection and, in a construction-to-permanent loan, the conversion to a regular mortgage. It is worth understanding one last risk here: if the finished home is appraised for less than it cost to build, you could face a gap between the loan and the property's value that you have to cover. Lining up your plans, budget, builder, and contingency carefully at the start is the best protection against surprises at the end. The figures above estimate the interest you will carry through the build and the payment you will settle into afterward.