Extra principal payments are the most powerful, most underused wealth-building move available to a homeowner. Every dollar of extra principal today skips the interest that would have accrued on it for the remaining life of the loan. The math is stark: an extra $200/month starting in year one can shave 7+ years off a 30-year loan and save over $100,000 in interest.
Worked example: $350,000 loan at 7% for 30 years. Base P&I $2,328. Add $300/month extra principal ($2,628 total). You pay the loan off in 22 years 4 months (7.7 years early) and save $116,400 in interest.
Why extra principal crushes invest-the-difference (sometimes)
At a 7% mortgage rate, every extra principal dollar earns a guaranteed 7% tax-free return. For that extra dollar to beat investing, you'd need an after-tax market return above 7%. The S&P 500 has averaged ~10% historically, but with volatility and taxes the after-tax real return is closer to 6-7%. At today's mortgage rates, extra principal is competitive with index investing on a risk-adjusted basis.
Biggest impact comes from year-one extras
A $10,000 extra principal payment in year 1 of a $350,000 / 7% / 30-year loan saves about $37,000 in interest over the loan's life. The same $10,000 in year 15 saves only about $7,000. Front-load extras whenever possible.
Forms the extra payment can take
- Fixed monthly extra — add a round number to each payment. Easiest to automate.
- Annual lump sum — tax refund, bonus, or year-end cash. Efficient if cash flow is variable.
- Round up — round $2,328 payment up to $2,400 or $2,500. Painless way to start.
- 13th payment — make a full extra payment once a year. Roughly equivalent to biweekly.
Pitfall: paying ahead without designating principal
Some servicers apply extra payments to the next month's payment instead of principal unless you specify. Write "PRINCIPAL ONLY" on the check or use the principal-only option in the servicer's portal. Verify the next statement shows the principal reduction, not an "account credit."