Amortization Calculator

Reading the schedule is the whole point, so start with the columns. Each row covers one payment. The interest column is the balance from the previous row multiplied by the monthly rate — it is rent on the money you still owe. The principal column is whatever is left of your payment after that interest is covered, and that is the part that actually shrinks the debt. The balance column carries the running total down the page until it hits zero on the final row.

Because interest is charged on the outstanding balance, the earliest rows are mostly interest and only a sliver of principal. As the balance falls, the interest charge falls with it, so a larger slice of the same fixed payment goes to principal each month. That is why equity builds slowly at first and then accelerates — the table makes the curve visible row by row.

An extra monthly payment is applied straight to principal. Because it removes balance early, it cancels all the future interest that balance would have generated, so even a modest extra amount can lop months off the term and reshape every row below it. The table and CSV update to show the shortened schedule.

Take a 200,000 loan at 6.5% over 30 years (360 months) with no extra payment. The level payment is about 1,264 a month. In month 1, interest is 200,000 × (6.5 ÷ 12 ÷ 100) ≈ 1,083, leaving only about 181 toward principal. The principal portion does not overtake the interest portion until around month 233 — roughly year 20 — which is when each payment finally builds more equity than it costs. Over the full term you pay about 255,089 in interest. Add 200 a month extra and the loan clears years early, erasing a large chunk of that interest.

At a 0% rate there is no interest column to speak of — every payment is pure principal and the balance falls in a straight line to zero. Watch the final row: it is deliberately trued up to absorb rounding, so it is often a few units smaller than the others rather than a clean repeat of the level payment. If you set an extra payment large enough, the loan can clear in a fraction of the nominal term, and the schedule simply stops at the real payoff month rather than running the full count.