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Construction Loan Calculator

Enter your loan amount, interest rate, construction period, and repayment term to calculate monthly payments, total interest, and a full post-construction amortization schedule.
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Luis GonzalezCreated by Luis GonzalezLast updated:

How to Use This Calculator

  1. 1

    Enter Loan Amount

    Input the total construction loan amount, such as $300,000.

  2. 2

    Set Interest Rate

    Enter the annual interest rate as a percentage.

  3. 3

    Enter Repayment Period

    Input the number of months over which you will repay the loan after construction is complete (e.g., 240 months for 20 years).

  4. 4

    Calculate

    Click Calculate to see the interest-only payment during construction, the full payment after construction, and total interest paid.

Example Calculation

A homebuilder takes a $300,000 construction loan at 5% interest with a 240-month (20-year) repayment period after construction.

Loan Amount

$300,000

Interest Rate

5%

Repayment Period

240 months

Results

Monthly Payment During Construction

$1,250.00 (interest only). Monthly Payment Post-Construction: $1,979.87. Total Interest Paid: $175,168.09.

Tips

Budget for Interest-Only Phase

During construction you only pay interest, which is significantly lower. Plan for the payment jump once full repayment begins.

Lock in Your Rate

Construction loan rates in 2025 average 6-8%. Try to lock in a rate before construction starts to avoid surprises.

Plan for Delays

Construction projects often run over schedule. Budget extra months of interest-only payments as a cushion.

The Construction Loan Calculator helps prospective homeowners and builders understand the two-phase cost structure of construction financing. By entering loan amount, interest rate, construction period, and repayment term, you get monthly payments for both phases, total interest, total cost, and an effective blended rate. For a $300,000 loan at 7.5% with 12 months of construction and a 20-year repayment, the post-construction monthly payment is $2,416.78 and total interest over the life of the loan is $302,527. Use these figures to plan your building budget in 2026.

How Construction Loan Payments Are Calculated

A construction loan has two distinct payment phases:

  1. During Construction (Interest-Only):

    • Monthly Interest Rate = Annual Interest Rate / 12 / 100
    • Monthly Interest Payment = Loan Amount Drawn x Monthly Interest Rate (Payments increase as more funds are drawn, up to the full loan amount.)

  2. Post-Construction (Fully Amortized):

    • Monthly Payment (M) = P [ i(1 + i)^n ] / [ (1 + i)^n - 1] Where:
    • P = Loan Amount (full amount after construction)
    • i = Monthly Interest Rate
    • n = Total Number of Repayment Months
💡 Understanding your total financial obligation is key to any loan. Use our Total Loan Cost Calculator to see all fees and interest over the loan's lifetime.

Estimating Payments for a New Home Build

Consider a borrower securing a $300,000 construction loan at 7.5% annual interest, with a 12-month construction period and 240-month (20-year) repayment.

  1. Monthly Interest Rate: Monthly Rate = 7.5% / 12 / 100 = 0.00625
  2. Monthly Payment During Construction (at full draw): Interest-Only Payment = $300,000 x 0.00625 = $1,875.00
  3. Monthly Payment Post-Construction (Amortized): M = $300,000 [ 0.00625(1 + 0.00625)^240 ] / [ (1 + 0.00625)^240 - 1] M = $2,416.78
  4. Total Construction Interest: $1,875.00 x 12 = $22,500
  5. Total Repayment Interest: ($2,416.78 x 240) - $300,000 = $280,027
  6. Total Interest: $22,500 + $280,027 = $302,527
  7. Total Cost of Loan: $300,000 + $302,527 = $602,527

The borrower pays up to $1,875 per month during construction, then $2,416.78 per month for 20 years. The payment jump at conversion is $542 per month.

💡 The interest component is a significant part of any loan. Use our Total Interest Paid Calculator for a detailed interest breakdown.

Types of Construction Loans

  1. Construction-to-Permanent: The most common option. The construction loan converts into a permanent mortgage upon completion, saving a second set of closing costs.
  2. Construction-Only: Covers only the build phase. Upon completion, the borrower secures a separate mortgage — two sets of closing costs but flexibility to shop for the best permanent rate.
  3. Owner-Builder: For borrowers acting as their own general contractor. Lenders require proven construction experience and more rigorous inspections.
  4. Renovation Loans (FHA 203k, HomeStyle): Combine purchase or refinance with renovation costs. Funds are released in draws as renovation milestones are met.

Structuring Your Construction Budget in 2026

Construction costs and financing rates fluctuate with the economy. In 2026, with construction loan rates in the 7.0-8.0% range, careful budgeting is essential:

  • Reserve a 10-15% contingency beyond your construction estimate for cost overruns, material price changes, and weather delays.
  • Lock your permanent rate early if your lender offers a rate lock during construction — this protects against rate increases before conversion.
  • Track draws carefully — each draw increases your interest-only payment. Align your draw schedule with your monthly budget to avoid cash flow surprises.
  • Consider a shorter repayment term — switching from 20 to 15 years increases monthly payments but significantly reduces total interest paid.

Formula Variants for Different Loan Structures

The standard Fixed-Rate Amortizing Loan uses:

Monthly Payment = P [ i(1 + i)^n ] / [ (1 + i)^n - 1]

where P is principal, i is the monthly interest rate, and n is the total number of payments.

A Construction Loan modifies this with two phases:

  1. Interest-Only on Drawn Funds: Interest Payment = (Drawn Amount) x (Annual Rate / 12) — payments start low and increase with each draw.
  2. Conversion to Amortized Loan: Once construction is complete, the full principal enters the standard amortization formula above.

Variable-Rate (ARM) Construction Loans use the same formulas but adjust the interest rate periodically based on a market index, causing monthly payments to fluctuate after conversion.

Frequently Asked Questions

How does a construction loan differ from a regular mortgage?

Construction loans typically have two phases: an interest-only phase during construction where you pay only interest on drawn funds, and a repayment phase after construction is complete where you make full principal-and-interest payments. Regular mortgages begin full repayment immediately.

Why are construction loan rates higher than mortgage rates?

Construction loans carry more risk for lenders because the collateral (the building) does not yet exist or is incomplete. There is also the risk of construction delays, cost overruns, and project abandonment. These additional risks are reflected in higher interest rates, typically 1-2% above standard mortgage rates.

What is the interest-only payment during construction?

During the construction phase, you only pay the interest accruing on the loan balance each month. This is calculated as (Loan Amount x Annual Rate) / 12. For a $300,000 loan at 5%, this would be $1,250 per month.

Can I convert my construction loan to a permanent mortgage?

Yes, many lenders offer construction-to-permanent loans (also called one-time-close loans) that automatically convert to a standard mortgage once construction is complete. This saves on closing costs and simplifies the process compared to obtaining two separate loans.