Mortgage Prepayment Calculator

How Prepayment Reduces Interest

Each extra principal payment immediately reduces the loan balance — eliminating future interest that would have accrued on that amount. $1,000 extra payment on a $300K loan at 6.5% in year 1 saves about $4,400 in interest over loan life. Earlier prepayment = larger interest saving. The same $1,000 prepayment in year 25 saves only $325. Time-value works exponentially in your favor early in the loan.

Three Common Prepayment Strategies

(1) Round up monthly payment: pay $1,650 instead of $1,587 = $63/month extra. Adds 4-6 years off 30-year loan. (2) Biweekly payments: half payment every 2 weeks = 13 monthly equivalents per year. Adds 4-5 years off. (3) Annual lump sum (tax refund, bonus): $5,000/year extra. Adds 8-10 years off. (4) One-time large prepayment: $20K early in loan can shorten by 3-5 years and save $40K-$80K interest.

The Investment Trade-off

Mortgage prepayment effectively earns guaranteed return equal to mortgage rate (e.g. 6.5%). Stock market historical return: ~10% nominal, ~7% real. Prepaying mortgage at 3% = clear loss vs investing. Prepaying at 7%+ = roughly even. Decision depends on: (1) Your risk tolerance, (2) Tax bracket (mortgage interest deduction subsidizes mortgage), (3) Other debt (always pay credit card debt first), (4) Cash flow needs. Many prefer prepayment for psychological freedom regardless of math.

Prepayment Penalty Risks

Most conventional mortgages no longer have prepayment penalties (banned for owner-occupied since 2014). Investment property loans, hard money, and some commercial loans may still have penalties (typically 2-5% of prepayment amount for first 3-5 years). Always check loan documents for prepayment penalty clause before making large extra payments. FHA, VA, USDA loans never have prepayment penalties.

Sources: CFPB Mortgage Servicing Rules, Dodd-Frank Act §1414. Last updated: May 2026.