A $200 extra payment changes the payoff date by 81 months
Jessica and Brian borrow $300,000 at 6% for 30 years. Their principal-and-interest payment is $1,798.65 a month. Paying another $200 toward principal every month from the first payment would clear the loan in month 279 instead of month 360, about six years and nine months earlier. On the stated fixed-rate model, lifetime interest falls from $347,514.57 to $256,341.13, a difference of $91,173.44. Taxes, insurance, fees and any prepayment charge are outside this example.
The prior version quoted a $34,300 saving and 5.5 years early for these same inputs. Those figures do not follow from the standard amortization formula. A borrower should check the balance schedule, not trust a rounded headline.
Follow one payment into the loan balance
Monthly interest is the opening principal × 0.06 / 12. The remainder of the $1,798.65 payment reduces principal. The interest portion falls as the balance falls; the contractual payment stays about the same. The table uses the exact unrounded payment internally and rounds each displayed amount to cents.
| Payment | Balance before payment | Interest | Principal from scheduled payment |
|---|---|---|---|
| 1 | $300,000.00 | $1,500.00 | $298.65 |
| 120 | $251,597.84 | $1,257.99 | $540.66 |
| 240 | $162,994.44 | $814.97 | $983.68 |
| 359 | $3,570.50 | $17.85 | $1,780.80 |
Scheduled payment shifts from interest to principal
The last scheduled payment at month 360 clears the remaining $1,789.70 plus about $8.95 interest. Servicers round installments and daily interest differently; expect small cents-level differences on a real statement.
What the $200 changes, and what it does not
With the extra principal paid from month 1, the amount used for principal reduction is the scheduled principal plus $200. That immediately lowers next month's interest. The $200 continues each month until month 279, when the remaining balance is cleared with a smaller final payment.
| Fixed 6% loan, $300,000 starting balance | Scheduled payment only | $200 extra principal monthly |
|---|---|---|
| Payoff month | 360 | 279 |
| Interest over the loan | $347,514.57 | $256,341.13 |
| Interest saved | — | $91,173.44 |
Lifetime interest on $300,000 at 6%
The $91,173.44 is avoided interest across the life of the loan. It is not free cash today. The household has to supply an additional $200 each month while the loan remains active. If that money would otherwise cover essential spending or higher-cost debt, the decision is different.
Timing changes the saving. If the household starts the same $200 extra principal payment only at month 121, after ten years of scheduled payments, the modeled loan ends in month 319 and total interest is $312,176.02. That still avoids $35,338.55 relative to the scheduled-only path, but far less than starting in month 1. Waiting until month 241 gives $339,935.32 lifetime interest and an end in month 345. The early balance is larger, so an early principal reduction prevents more future interest.
| First month with $200 extra | Final month | Lifetime interest |
|---|---|---|
| None | 360 | $347,514.57 |
| Month 1 | 279 | $256,341.13 |
| Month 121 | 319 | $312,176.02 |
| Month 241 | 345 | $339,935.32 |
Check your servicer's handling before you automate it
Ask how to mark an extra payment as principal-only and confirm the new balance on the next statement. Some servicers advance the next due date when you pay extra; you still need to meet each scheduled payment. Review your note for a prepayment penalty. In the US, penalties depend on the loan contract and are restricted for many mortgages; there is no universal 10% or 20% annual allowance.
If you pay half a monthly installment every two weeks, check when the servicer actually credits the money and whether a third-party service charges a fee. Twenty-six half-payments equal thirteen monthly payments in a year, but a servicer that holds partial payments can change the timing advantage. The CFPB mortgage guidance explains how principal and interest change through the term.
Your actionable check is the next statement: the balance should fall by the scheduled principal plus the extra amount, after the month's interest is accounted for.
Keep an emergency reserve before locking all spare cash into home equity. A principal prepayment normally cannot be withdrawn on demand; getting money back may require a sale, refinance or new loan. Compare the mortgage with any higher-cost debt you have, the value of liquidity, and your loan's tax situation. None of those trade-offs change the amortization arithmetic, but they determine whether the extra payment is useful for your household.
One short audit can catch a fake amortization table. The fixed-payment formula gives $1,798.6516 per month for $300,000 at 6% over 360 months. In the first 60 scheduled payments, the household sends about $107,919.09: $87,082.16 goes to interest and $20,836.93 reduces principal, leaving $279,163.07. A table claiming the balance falls by $50,000 in five years without extra payments is inconsistent with these inputs. The same check works on your loan: opening balance minus cumulative principal paid should equal the statement balance, subject to rounding, fees and any escrow line kept separate.
Do not add an escrow deposit to principal-and-interest when testing the formula. Property tax and homeowners insurance may make the amount withdrawn from a bank account larger than $1,798.65, but those dollars do not amortize the $300,000 debt. Separate escrow from the lender's interest and principal columns before comparing statements with this example.
