How the 13th Mortgage Payment Strategy Works
The 13th Mortgage Payment Strategy is a straightforward financial technique where a homeowner makes one extra monthly principal payment each year. On a standard 30-year fixed loan, this simple habit can shorten your loan term by over 4 to 5 years and save tens of thousands of dollars in interest.
This guide explains how extra principal payments work, compares implementation methods, and demonstrates the compounding savings using our Mortgage Overpayment Calculator.
Why One Extra Payment Has Such a Huge Impact
During the first 10 to 15 years of a 30-year mortgage, the vast majority of your monthly payment goes toward interest, while only a small fraction reduces your actual principal balance.
When you designate an extra payment specifically as "Principal Only", 100% of those dollars bypass interest and directly reduce the underlying loan balance. This lowers the base balance used to calculate next month's interest charge.
Standard Payment: $1,500 ($1,100 Interest + $400 Principal)
Extra 13th Payment: $1,500 ($0 Interest + $1,500 Direct Principal Reduction)
3 Ways to Structure the 13th Payment
- The Annual Lump-Sum Method: Use an annual tax refund, work bonus, or savings to make one full extra payment during a specific month (e.g., every January).
- The Monthly 1/12th Add-On: Divide your regular monthly principal and interest payment by 12, and add that fraction to every monthly payment.
- Example: If your monthly payment is $1,800, add $$1,800 / 12 = $150$ per month.
- Biweekly Payroll Deduction: Set up automated biweekly transfers equal to half your monthly payment (26 half-payments = 13 full payments per year).
Savings Example: $250,000 Loan at 6.0% Interest
| Metric | Standard 30-Year Loan | With 13th Payment ($1,498/yr) | Difference / Savings |
|---|---|---|---|
| Monthly Payment | $1,498.88 | $1,498.88 + $125/mo | +$125 / month |
| Total Interest Paid | $289,595 | $223,810 | $65,785 Saved |
| Total Loan Term | 360 Months (30 Yrs) | 304 Months (25.3 Yrs) | 4.7 Years Early |
Calculate Your Custom Principal Savings
See how making extra monthly, annual, or biweekly overpayments reduces your mortgage term using our free Mortgage Overpayment Calculator. Explore more tools in our Finance Category.
For details on automated biweekly schedules, see Biweekly Mortgage Payments: How to Cut Loan Term.
