Educational only. Rate examples reflect 2026 Freddie Mac PMMS averages. Your actual rate depends on credit, LTV, and lender.
Most people understand "my mortgage payment is $2,500/month" and stop there. They miss the fact that of that $2,500, almost all of it is interest in year one — and that one specific behavior (extra principal, applied early) can save them six figures.
Build your own schedule in the Amortization Calculator. This guide explains what you're looking at.
The formula, in plain English
A fully-amortizing loan splits each payment into two pieces: interest (your balance × monthly rate) and principal (everything else). The payment itself is fixed. Each month your balance shrinks slightly, so next month's interest is slightly smaller, so the principal portion is slightly larger. Compound that 360 times on a 30-year mortgage.
The shocking year-1 math
$400,000 mortgage, 7% rate, 30-year term. P&I payment: $2,661/month. Of your first payment, $2,333 is interest and $328 is principal. After 12 months you've paid $31,932 to the bank but only knocked $4,053 off the balance. After 5 years: $159K paid, $377K balance. After 10 years: $319K paid, $343K balance. The loan is back-loaded with principal — by design.
Why an extra $200/month changes everything
Same loan, but you add $200/month to every payment. That $200 hits principal directly. The $200 also avoids ~7% interest for the remaining life of the loan — and the savings compound. Result: the loan pays off in 23.5 years instead of 30 and you save ~$112,000 in interest. For an extra $200/month.
The earlier you start, the bigger the impact. A $200/month extra payment in year 1 saves ~30× more interest than the same $200 in year 25.
Bi-weekly payments: the painless hack
Pay half your monthly mortgage every 2 weeks instead of full monthly. There are 52 weeks/year = 26 half-payments = 13 full monthly equivalents (vs 12). That extra payment hits principal. On a 30-year mortgage at 7%, bi-weekly knocks the term down to ~25 years and saves $80K+ in interest — without ever paying more than a half-payment at a time.
Caveat: some lenders charge a setup fee for "official" bi-weekly programs. Don't pay it. Just send the extra payment manually once a year, or break it into monthly extra-principal.
Recasting vs paying extra: not the same
- Extra monthly principal: Loan pays off earlier. Monthly payment stays the same.
- Recast (lump sum + re-amortize): Loan still pays off on original date, but monthly payment drops. Used when you want lower required payment but still own the home for the full term.
For total interest minimization: extra monthly principal wins by a huge margin. Recasting reduces optionality without saving much interest.
When NOT to pay extra on the mortgage
Hierarchy of capital allocation, roughly:
- Capture full 401(k) employer match (often 50–100% guaranteed return).
- Pay off any debt above ~9% rate (credit cards, personal loans).
- Build 3-month emergency fund in HYSA.
- Max HSA if eligible.
- Roth IRA / continue 401(k) to limits.
- Then — and only then — extra mortgage principal vs taxable brokerage. At 7% mortgage and 30% marginal tax, the after-tax mortgage cost is ~5%. S&P 500 long-run is ~7% real. Math is close; emotional comfort with debt-free can tip it.