Construction Loan Calculator

The Construction Loan Calculator estimates the interest-only payments you make on staged draws while your home is being built, then the fully amortizing monthly payment once construction is finished and the loan converts to a permanent mortgage. Unlike a basic mortgage calculator, it models how your payment ramps up as the builder draws more money, lets you compare even, front-loaded, and back-loaded draw schedules, and shows the total construction interest alongside the long-term mortgage cost on a single timeline.

What Is a Construction Loan?

A construction loan is short-term financing used to build a new home or carry out a major renovation. Instead of handing over the full amount at closing like a regular mortgage, the lender releases the money in stages called draws as the builder completes milestones — for example the foundation, framing, roofing, mechanicals, and final finishes. You pay interest only on the money that has actually been drawn, so payments are small at the start and grow as the project advances.

How Construction Loan Payments Work

During the build, each month's payment is simply the interest on your outstanding (drawn) balance. Because that balance climbs with every draw, the interest-only payment climbs too, peaking just before completion. When the home is finished, the loan is repaid or converted into a long-term mortgage, and you begin making standard principal-and-interest (P&I) payments.

Construction Loan Formulas

In Step 3, \(P\) is the loan amount, \(i\) is the monthly permanent rate (annual rate ÷ 12), and \(n\) is the number of monthly payments (years × 12). This is the same amortization formula used by a standard mortgage calculator.

How Draw Timing Is Counted

The calculator assumes each month's draw lands at the start of that month. Interest for that month is charged on the full balance drawn so far, including that month's draw. Every month of the build is counted, so the total construction interest reflects the full construction period.

Why the Draw Schedule Matters

Because interest accrues only on the amount drawn, the timing of your draws changes the total construction interest you pay:

Construction-to-Permanent vs. Stand-Alone Construction Loans

Typical Construction Draw Schedule

Lenders and builders agree a draw schedule before work begins. A common five-stage residential schedule looks like this:

Exact percentages vary by lender and project; this calculator models the timing as even, front-loaded, or back-loaded so you can bracket the likely interest cost.

How to Use This Calculator

1. Enter your project numbers: Type the total project cost (land + build) and your down payment. The loan amount is the difference.
2. Set the construction terms: Enter the construction interest rate, the build period in months, and pick a draw schedule pattern.
3. Set the permanent mortgage terms: Enter the rate and term of the long-term loan that begins once the home is finished.
4. Click Calculate: Review the interest-only payment ramp, the permanent monthly payment, total interest for both phases, and the full month-by-month draw schedule.

Frequently Asked Questions

How does a construction loan work?

A construction loan releases money in stages called draws as building milestones are reached, such as foundation, framing, and finishes. During construction you pay interest only on the amount drawn so far, so your payment starts small and grows as more of the loan is released. Once the home is finished the loan either converts to a permanent mortgage or is refinanced into one.

How are construction loan payments calculated?

During construction, each month's payment equals the cumulative amount drawn multiplied by the monthly interest rate (annual rate ÷ 12). Because the drawn balance rises over time, the interest-only payment ramps up. After construction, the permanent payment is a standard amortizing mortgage: M = P × i × (1 + i)ⁿ / ((1 + i)ⁿ − 1), where P is the loan amount, i is the monthly rate, and n is the number of months.

What is a construction-to-permanent loan?

A construction-to-permanent loan is a single loan that funds the build with interest-only draw payments and then automatically converts to a long-term mortgage when the home is complete. It is convenient because you close once and pay one set of closing costs, unlike a stand-alone construction loan that must be refinanced into a separate mortgage afterward.

Why does my construction payment increase each month?

You are charged interest only on the money that has actually been drawn from the loan. Early in the build only a small portion has been released, so the interest-only payment is low. As the builder hits more milestones and draws more funds, the outstanding balance grows and so does the interest-only payment, peaking just before the home is finished.

Does the draw schedule change how much interest I pay?

Yes. Because interest accrues on the drawn balance, front-loaded draws (more money released early) accrue more total construction interest, while back-loaded draws (more money released late) accrue less. An even draw schedule sits in between and roughly matches the common rule of thumb that you pay interest on about half of the loan over the construction period.

How much down payment do I need for a construction loan?

Construction loans typically require a larger down payment than a standard mortgage, often 20% to 25% of the total project cost, because they are considered higher risk. Some government-backed programs allow less. This calculator lets you enter any down payment so you can see how it changes your loan amount and payments.

Additional Resources

• Amortizing Loan - Wikipedia