Guide · 7 min read
What Extra Mortgage Payments Actually Save
An extra payment does two things at once: it shortens the loan and it cuts the interest bill. The second effect is much larger than most people expect, and the first is what you feel.
On a $400,000 loan at 6.9%, an extra $200 a month cuts five years and nine months off the term and removes about $124,000 of interest.
A fixed-rate mortgage spreads a fixed total over a fixed number of months. Every payment covers the interest that accrued that month and puts the remainder toward principal. Early in the loan almost all of the payment is interest; late in the loan almost all of it is principal.
That shape is why extra payments are so effective early on. Money that goes to principal in year two stops accruing interest for the remaining 28 years. The same money paid in year 25 saves very little, because there is barely any interest left to avoid.
A worked example
Take a $400,000 loan at 6.9% over 30 years. The monthly principal-and-interest payment is $2,634. Over the full term you would pay $948,384 in total — $548,384 of it interest.
Now add $200 a month, applied to principal. The payment becomes $2,834 and the loan closes five years and nine months early, in January 2051 instead of October 2056. Total interest falls to $424,802.
Where the money should go instead
Extra principal earns you the mortgage rate, risk-free and tax-free. That is a real return, and at 6.9% it is a good one. But it is not automatically the best one available.
The comparison that matters is against other uses of the same money, adjusted for risk and liquidity. Paying down a 6.9% mortgage is equivalent to buying a risk-free 6.9% bond that you cannot sell. If you have credit card debt at 22%, paying that first is a better trade. If you have no emergency fund, building one first is better, because a paid-down mortgage cannot cover a lost job.
- Credit card or personal loan above the mortgage rate — pay that first, always.
- No emergency fund — build three to six months of expenses before adding principal.
- Employer 401(k) match you are not taking — that is an immediate 50–100% return and beats any mortgage.
- High-interest savings or CDs paying less than the mortgage — the mortgage wins on after-tax return.
- Everything above is handled — extra principal is a sound default.
How to make the payment count
A mortgage servicer applies payments according to the instructions attached to them. A payment with no instruction may be held in a suspense account, applied to next month, or applied to interest — all of which defeat the purpose.
Mark the payment "apply to principal" and confirm it on the next statement. Most servicers let you set this once for recurring extra payments, but the first one is worth checking.
Check the prepayment penalty first
Most US mortgages have no prepayment penalty, but not all. A penalty can be a fixed fee, a percentage of the balance, or a rule that you lose interest for a set number of months. Read the note before you start paying extra.
If there is a penalty, it usually expires after a set period — often three to five years. Waiting it out is often cheaper than paying it.
Frequently asked questions
Does an extra payment go to principal automatically?
Not always. Servicers vary, and some will apply it to the next scheduled payment unless you specify otherwise. Mark it explicitly and verify on the statement.
Is it better to pay extra monthly or in a lump sum?
Earlier is better, so a lump sum now beats the same total spread over a year. But only slightly, and the monthly habit is easier to keep. Choose based on what you will actually sustain.
Will paying extra lower my required monthly payment?
No. Extra principal shortens the term, not the payment. To lower the payment you would need to recast or refinance, which are different transactions with their own costs.