How to Calculate Mortgage Payments for Construction-to-Permanent Loans with Interest-Only Build Phase

Understanding Construction-to-Permanent Loans with Single Close

A construction-to-permanent loan with single close combines two financing stages into one streamlined transaction. You close once, pay one set of closing costs, and undergo one credit check—then your construction financing automatically converts to a permanent mortgage when building ends.

Here's how single-close construction-to-permanent loans work:

• Phase 1 (Construction): Interest-only payments on disbursed funds for 6-12 months
• Phase 2 (Permanent): Standard principal and interest payments for 15-30 years

According to U.S. Census Bureau data, the median time to complete new single-family home construction was 7.7 months as of 2023—making most construction phases fall within the standard 12-month window.

Qualification requirements for single-close construction loans:

• Credit score: 620-680 minimum, with most lenders preferring 680+
• Down payment: 10-20% of total project cost (compared to 3-5% for conventional purchases)
• DTI ratio: Typically 43% maximum, calculated using the fully amortized permanent payment
• Builder requirements: Licensed, insured contractor approved by your lender

Total closing costs on construction-to-permanent loans typically run 3-6% of the loan amount—higher than standard mortgages due to additional inspections and specialized appraisals costing $500-$1,500.

How Interest-Only Payments Work During the Construction Phase

During construction, you don't make full mortgage payments. Instead, you pay interest only on the funds actually disbursed to your builder—not the total loan amount. This is where many first-time construction borrowers miscalculate their budget.

The draw schedule determines your payment increases:

Lenders release funds in stages (called "draws") as construction progresses. A typical draw schedule looks like this:

• Draw 1: 15% at foundation completion
• Draw 2: 25% at framing completion
• Draw 3: 25% at rough mechanical (plumbing, electrical, HVAC)
• Draw 4: 20% at interior finishing
• Draw 5: 15% at final completion

Each draw requires an inspection (costing $300-$800 each, with 4-6 inspections typical during the build phase) before the lender releases additional funds.

Key rate considerations:

Construction loan interest rates run 0.5-1.5 percentage points higher than conventional mortgage rates during the build phase. If current 30-year fixed rates are 7.0%, expect construction phase rates of 7.5-8.5%.

Common misconception: Many borrowers believe monthly payments stay constant during construction. Reality: Your interest-only payment increases each time a new draw is disbursed. Month one might cost $312; month eight might cost $1,875 on the same loan.

Another critical point: While monthly payments are lower during the interest-only period, you're not building equity. No principal reduction occurs until the permanent phase begins.

Step-by-Step: Calculating Your Construction Phase Interest-Only Payments

Use this formula to calculate your interest-only payment at any point during construction:

Monthly Interest Payment = (Amount Disbursed × Annual Interest Rate) ÷ 12

Example calculation for a $400,000 construction loan at 8.0% interest:

After Draw 1 (15% disbursed = $60,000):

($60,000 × 0.08) ÷ 12 = $400/month

After Draw 2 (40% disbursed = $160,000):

($160,000 × 0.08) ÷ 12 = $1,067/month

After Draw 3 (65% disbursed = $260,000):

($260,000 × 0.08) ÷ 12 = $1,733/month

After Draw 4 (85% disbursed = $340,000):

($340,000 × 0.08) ÷ 12 = $2,267/month

After Draw 5 (100% disbursed = $400,000):

($400,000 × 0.08) ÷ 12 = $2,667/month

Total estimated interest paid during 8-month construction: Approximately $11,500-$13,000 (varies based on draw timing)

Budget planning tip: Calculate your maximum interest-only payment (full disbursement) and ensure it fits your DTI ratio. Lenders typically qualify you based on the permanent phase payment, but you need cash flow for rising construction payments too.

Interest-only payments during the construction phase typically range from $400-$2,500+ monthly depending on the amount disbursed and current rates.

Construction-to-Permanent Loan vs Traditional Construction Loan Payment Comparison

Cost comparison example ($400,000 total project):

• Single-close total fees: $16,000-$24,000
• Two-close total fees: $24,000-$48,000
• Potential savings with single-close: $8,000-$24,000

Note: Some states require separate construction and permanent loan transactions, particularly judicial foreclosure states. Recording fees and transfer taxes vary significantly—from under $100 in Missouri to over $1,000 in New York.

Calculating Your Permanent Phase Mortgage Payment

Once construction completes, your loan converts to a standard amortizing mortgage. Your permanent payment includes principal, interest, taxes, and insurance (PITI).

Permanent phase payment formula:

M = P × [r(1+r)^n] ÷ [(1+r)^n – 1]

Where: M = monthly payment, P = principal balance, r = monthly interest rate, n = total payments

Example: $400,000 loan at 7.0% for 30 years:

• Principal & Interest: $2,661/month
• Property taxes (estimated): $400/month
• Homeowners insurance: $150/month
• Total PITI: $3,211/month

DTI calculation for qualification:

With a $3,211 PITI payment and maximum 43% DTI, you'd need minimum gross monthly income of $7,467 ($89,600 annual) with no other debts. Add a $500 car payment, and required income jumps to $8,630 monthly ($103,560 annual).

Rate adjustment opportunity: While single-close loans lock your permanent rate upfront, some programs allow a one-time rate adjustment if rates drop during construction. Ask your lender about float-down provisions before closing.

Lower down payment options: FHA construction loans allow down payments as low as 3.5%, and certain conventional programs accept 10% down—contrary to the misconception that 20% is always required.

Frequently Asked Questions About Construction-to-Permanent Loan Payments

Do I pay interest on the full loan amount during construction?

No. You pay interest only on funds actually disbursed to your builder. If $100,000 of a $400,000 loan has been drawn, you pay interest on $100,000 only. Payments increase as additional draws occur throughout construction.

Can I lock my interest rate for the permanent mortgage at closing?

Yes. Single-close construction-to-permanent loans lock your permanent mortgage rate when you close—protecting you from rate increases during the 6-12 month build phase. Some programs also offer float-down options if rates decrease.

What happens if construction takes longer than expected?

Most single-close construction loans include a 12-month construction window. Extensions may be available but often require additional fees and lender approval. Budget for potential delays by ensuring your finances can handle extended interest-only payments.

Calculate Your Construction-to-Permanent Loan Payment Today

Ready to calculate your construction-to-permanent loan payments? Use our free mortgage calculator at QuickMortgageCalc.com to estimate both your interest-only construction phase payments and your permanent monthly mortgage amount. Enter your total project cost, expected interest rate, and loan term to see exact payment projections for every stage of your build.

Get accurate numbers before you break ground—calculate your construction loan payment now.