Finance
Amortization schedule
The schedule is where a loan stops being one number and starts being a story about how slowly the balance moves at the beginning.
Payment schedule
How each payment is split
principalk = payment − interestk
The payment is constant, but its composition is not. Interest is charged on whatever is still outstanding, so as the balance falls the interest portion falls with it and the principal portion grows to fill the gap. The schedule above is simply this calculation repeated until the balance reaches zero.
On a 30-year loan the split starts badly. At 6% on $250,000, the first payment is $1,250 interest and $249 principal. It takes until month 222 — year 19 — for principal to overtake interest.
Why overpaying early works so well
An extra payment goes entirely against principal. That principal would otherwise have accrued interest every month until the end of the term, so paying it now cancels the whole remaining stream. One extra $250 in month one of a 30-year loan at 6% saves about $1,260 in interest. The same $250 in month 300 saves around $12.
Add $250 every month from the start and the loan clears in roughly 22 years instead of 30, cutting total interest by about a third. The calculator shows both figures when you enter an extra amount.
Read the schedule before you refinance
Refinancing into a new 30-year loan resets you to the beginning of the curve, where almost the whole payment is interest. Someone eight years into a mortgage who refinances to a lower rate but a fresh 30-year term can end up paying more in total despite the better rate.
The fix is to compare like with like: run the remaining balance over the remaining term at the new rate, not over a new full term. If the payment is the constraint, take the longer term but keep overpaying.
Check for prepayment restrictions first
Most mortgages allow unlimited overpayment, but not all. Some fixed-rate deals cap annual overpayments at 10% of the balance, and some loans carry an explicit prepayment penalty in the first few years. On personal and auto loans, precomputed interest contracts mean paying early does not reduce interest at all unless a rebate clause applies.
Also confirm that your lender applies extra money to principal rather than holding it as an advance payment. It is worth a phone call — the difference is the entire benefit.
Common questions
Should I make one extra payment a year or pay a bit more monthly?
Monthly is marginally better because the principal reduction starts earlier, but the difference is small. Both approaches on a 30-year loan typically remove four to six years. Pick whichever you will actually keep doing.
What is a biweekly payment plan?
You pay half the monthly amount every two weeks, which produces 26 half-payments — the equivalent of 13 monthly payments a year. It shortens a 30-year mortgage by roughly four years. You can replicate it for free by dividing your payment by 12 and adding that to each month; paid third-party biweekly services rarely justify their fee.
Why is my final payment a different amount?
Rounding. The scheduled payment is rounded to the cent, so tiny discrepancies accumulate over hundreds of months. The last payment absorbs the difference and is usually a few dollars off.
Does an extra payment lower my monthly payment?
Not normally. It shortens the term instead. Some lenders offer recasting, where they recalculate the payment against the reduced balance over the original term — usually for a fee of a few hundred dollars. That lowers the payment but keeps you paying for the full period.