Calculate your monthly interest-only payments during the construction draw period. This calculator computes payments on each draw as funds are released, plus your total interest cost over the entire construction phase.
Interest-Only Payment Summary
Draw-by-Draw Schedule
| Draw # | Draw % | Draw Amount | Balance | Interest Payment |
|---|
Construction Loan Interest Only Calculator
What This Calculator Does and Why It Matters
A construction loan works differently from a regular mortgage. Rather than receiving the full amount upfront, funds are released in stages — called draws — as your project reaches specific milestones. During this period, you pay interest only on the money that has been drawn down, not on the total loan amount. This means your payments start small and grow as more money is released.
This free construction loan interest only calculator lets you map out exactly how much you will owe each month across your full draw schedule. It computes the interest payment after each draw, shows your growing balance, and totals your full interest cost before the loan converts to a permanent mortgage. For a broader view of your project budget, the Custom Home Builder Fee Calculator can help you estimate builder fees alongside your financing costs.
How to Use This Calculator
Step-by-Step Instructions
- Enter the total approved construction loan amount in dollars.
- Enter the annual interest rate quoted by your lender (as a percentage).
- Enter the total construction period in months (typically 9 to 18 months).
- Enter your draw schedule as percentages separated by commas — for example, if draws are 10%, 25%, 25%, 20%, and 20%, type: 10,25,25,20,20. The percentages must add up to 100.
- Click Calculate to see a full draw-by-draw table with interest payments and running balance.
- Use Reset to clear all inputs and start a new scenario.
The Formula Explained
Breaking Down the Formula
The interest-only payment for each draw period is simple: Payment = Outstanding Balance × Monthly Interest Rate. The monthly rate is your annual rate divided by 12. Because the balance grows with each draw, the payment also increases over time. At the end of the construction period, the full outstanding balance converts to your permanent mortgage.
For example, if your loan is $400,000 at 7.5% annual interest (0.625% per month) and your first draw is 15% of the loan ($60,000), your first monthly payment is $60,000 × 0.00625 = $375. After the second draw adds another $100,000, your balance becomes $160,000 and your payment rises to $1,000 per month.
Example Calculation with Real Numbers
A $500,000 construction loan at 7.5% over 12 months with draws of 10%, 20%, 20%, 20%, 15%, and 15% (six draws over six periods). The initial draw is $50,000, generating a $312.50 interest-only payment. By the final draw the cumulative balance is the full $500,000, with a monthly payment of $3,125. Total interest across all periods in this scenario is approximately $12,900 — a figure that is easy to overlook when budgeting only for the eventual mortgage payment. Builders working on smaller projects can also review the House Plan Estimate Calculator for Owner Builders to align their total budget projections.
When Would You Use This
Real Life Use Cases
Construction loans are used for new home builds, major additions, custom commercial buildings, and ground-up development projects. Any time a lender releases funds in phases rather than as a lump sum, understanding the interest accumulation on each draw is important for cash flow management. According to the Consumer Financial Protection Bureau (CFPB), construction loans typically carry higher interest rates than permanent mortgages and require careful planning to avoid cost overruns during the build phase.
Specific Example Scenario
A family is building a $650,000 custom home. Their lender approves a construction loan at 8.25% with a 14-month build schedule. Using this calculator, they map out five draw periods and discover their total interest cost during construction will be approximately $28,000. This lets them factor that cost into their overall budget before breaking ground rather than being surprised by it mid-project. For those comparing financing options, the FHA vs Conventional Loan Comparison Calculator can help evaluate what the permanent mortgage will look like once the construction phase ends.
Tips for Getting Accurate Results
Match Your Draw Schedule to Your Lender’s Actual Timeline
Lenders often tie draws to specific project milestones — foundation complete, framing complete, rough-in complete, and so on. Use the draw percentages your lender has already specified in your loan agreement rather than guessing. If you have not finalized the draw schedule, ask your loan officer for the standard breakdown they use.
Account for Rate Adjustments on Variable-Rate Loans
Many construction loans have variable interest rates tied to the prime rate or SOFR. If your loan rate can change during the construction period, run multiple scenarios using different rate assumptions to understand your best-case and worst-case payment ranges. A half-point rate increase on a $600,000 balance adds $250 per month to your interest payment.
Include Interest Reserve in Your Budget
Some lenders allow you to include an interest reserve — a portion of the loan set aside to pay the interest-only payments automatically. This means no out-of-pocket interest payments during construction, but it also means a higher outstanding balance at conversion. Run this calculator both with and without an interest reserve to see how it affects your permanent mortgage starting balance.
Frequently Asked Questions
What is an interest-only construction loan?
A construction loan that charges interest only on the funds that have been drawn, not the total loan amount. This keeps payments lower during the build phase. Once construction is complete the loan either converts to a permanent mortgage or you refinance into a traditional home loan.
How is a construction loan different from a mortgage?
A mortgage is issued for an existing property and begins amortizing immediately. A construction loan is issued for a project not yet built, disburses funds in stages, requires interest-only payments during the build, and typically has a shorter term (12 to 24 months) before it must convert or be repaid.
What happens to the loan after construction is finished?
Most construction loans either automatically convert to a permanent mortgage (called a construction-to-permanent or one-time-close loan) or require you to pay off the construction loan by refinancing into a new mortgage. The full outstanding balance — including any accrued interest added to principal — becomes the starting balance of your permanent loan.
Do I pay interest on the full loan amount from day one?
No. You only pay interest on the portion of the loan that has been drawn. If your total loan is $500,000 but only $100,000 has been disbursed so far, you pay interest on $100,000. This is one of the advantages of a draw-based construction loan compared to receiving a lump sum.
What is a draw schedule?
A draw schedule is the planned sequence of fund disbursements tied to construction milestones. Each draw releases a portion of your approved loan amount as the builder completes specific phases — such as foundation, framing, rough mechanical work, drywall, and final completion. Your lender will typically inspect the work before releasing each draw.
What interest rate should I use in this calculator?
Use the actual rate quoted in your construction loan commitment letter. Construction loan rates are often 1% to 2% higher than conventional mortgage rates and may be variable. If your rate is adjustable, use the current rate for a base estimate and then run a higher-rate scenario to stress test your budget.
Can I use this calculator for a commercial construction loan?
Yes. The formula for interest-only payments is the same whether the loan is residential or commercial. Commercial loans may have different draw structures, inspection requirements, and fee schedules, but the core interest calculation — balance × monthly rate — is identical.
What happens if construction takes longer than the loan term?
If construction runs over the agreed timeline, you may need to request an extension from your lender. Most lenders will grant short extensions but may charge fees or adjust the interest rate. It is important to build a buffer into your timeline estimate and budget for potential extension costs before applying for the loan.
Conclusion
Understanding your construction loan interest payments before the project starts is one of the most important steps in planning a successful build. This free construction loan interest only calculator makes it easy to see exactly how your payments grow with each draw, what your total interest cost will be, and what balance will convert to your permanent mortgage. Use it alongside other project budgeting tools to get the clearest possible picture of your total construction financing costs before you commit to a loan.