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Mortgage Self-Buydown Calculator

See how extra principal payments may shorten your mortgage and compare the resulting interest cost with a lower-rate mortgage.

Use this calculator to test how recurring extra principal payments, annual additions, or a one-time lump sum may change the life of a fixed-rate mortgage. The result compares the original amortization schedule with the accelerated schedule and estimates the total interest and time saved.

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Mortgage Self-Buydown Calculator

See how additional principal payments may reduce total interest and shorten the payoff timeline. The “interest-cost equivalent rate” compares your projected total interest with a standard loan at a lower rate; it does not change your contractual mortgage rate.

Applied every 12th payment.

What is a mortgage self-buydown?

A self-buydown is an educational comparison for a borrower who plans to pay more principal than the scheduled amount. Extra principal reduces the balance on which future interest is calculated, but the note rate remains unchanged.

How the interest-cost equivalent rate works

The calculator finds the lower fixed rate that would produce approximately the same total interest over the original loan term if no extra payments were made. It is a comparison metric—not a refinance quote, annual percentage rate, or modification of the loan.

Frequently asked questions

Do extra principal payments lower my mortgage rate?

No. They reduce the outstanding balance and may reduce future interest, but the contractual interest rate remains the same.

What is the interest-cost equivalent rate?

It is the fixed rate that would create approximately the same total interest over the original term without extra payments. It is only a comparison.

Will my servicer apply every extra payment to principal?

Servicer practices and loan terms vary. Confirm how to designate extra principal and whether any restrictions or prepayment terms apply.

Important: Calculators provide estimates for educational purposes only and are not loan offers, legal advice, tax advice, or guarantees. Actual payments, taxes, insurance, appreciation, closing costs, lender requirements, and Homebuyer Reward eligibility may differ. Extra principal payments do not change your contractual interest rate. Confirm payment application and any prepayment terms with your loan servicer.

How to use the result responsibly

The contractual rate on the mortgage does not change when you pay extra principal. The calculator’s interest-cost equivalent rate is a comparison: it estimates the lower fixed rate that would produce a similar total interest cost over the original term without the extra payments.

  • Confirm that the servicer applies additional funds to principal.
  • Check the loan documents for prepayment terms or restrictions.
  • Keep emergency savings and other financial priorities in mind before committing to an aggressive payoff plan.
  • Recalculate when the payment amount, start date, or planned lump sum changes.

Read the Guide to Extra Mortgage Payments for a fuller explanation, or use the Complete Mortgage Payment Calculator to estimate the normal monthly housing payment first.