Loan Amortization Calculator

Each month: interest = balance × rate; principal = EMI − interest; balance −= principal (prepayments come straight off the balance).

Reading an amortization schedule

Amortization is how a level-payment loan is repaid: each instalment is the same, but it is quietly split between interest (charged on the outstanding balance) and principal (what is left to reduce the debt). The schedule below lays out that split for every month, with the opening and closing balance, so you can see exactly where each payment goes and how the balance melts away. It shows year-end months by default; expand it to every month, or download the lot.

Because interest is charged on the balance — highest at the start — early payments are mostly interest and barely dent the principal. As the balance falls, the interest portion shrinks and more of each fixed payment attacks the principal, so the loan clears faster and faster toward the end.

Worked example — $300,000 at 6% over 30 years ($1,799 a month): Month 1: $1,500 interest, only $299 principal. Midway: roughly half and half. Final months: almost entirely principal, with a few dollars of interest.

The crossover month

There is a specific moment — the crossover — when a payment first puts more toward principal than interest. Before it, the bank is getting the larger share of every instalment; after it, you are. On a typical 30-year loan it falls surprisingly late, often past the halfway point in time, which is why the back half of a long loan pays down so much faster than the front half.

The crossover is one of the most useful things an amortization schedule reveals, and it is the headline statistic here. Prepaying brings it forward dramatically.

Prepayments change everything

A prepayment comes straight off the balance, so every future month’s interest is calculated on a smaller number. Add a recurring extra payment or a one-time lump and the schedule recomputes from that point: the balance drops faster, the crossover arrives sooner, and the loan finishes early. The calculator reports the interest saved and the new payoff time.

The effect is largest early in the loan, when the balance — and therefore the interest being charged — is at its peak. The same prepayment made in the final years saves comparatively little.

What this version covers

This calculator amortises a fixed-rate monthly loan with optional prepayments and a processing fee, and the schedule downloads to CSV for your own records or tax workings. A couple of specialised features — dating each row from a start date, and a rate-change schedule for floating-rate loans — are not included here.