🏦 Loan / Amortization Calculator

The amortisation behind the schedule

One level payment is worked out from the standard fixed-rate formula, then the schedule is walked a month at a time. Interest is charged on the balance that is actually left, so the principal share of every payment grows as the balance falls.

i = (rate / 100) / 12

payment = principal × i / (1 - (1 + i)^-months)      (at 0%: principal / months)

each month:  interest  = balance × i
             principal = payment - interest + extra
             balance   = balance - principal

$10,000 at 6% over 12 months gives a payment of $860.66. Month one charges 10,000 × 0.005 = $50.00 interest, leaving $810.66 off the balance and $9,189.34 owing. Run to the end it costs $327.96 in interest, $10,327.96 in all.

The extra payment box, and the last row

Anything you put there is added to the principal share of every month. On the same loan, $100 extra clears it in 11 months instead of 12 and drops the interest to $295.77 — $32.19 saved. The schedule opens on the first twelve months; Show all months expands it.

• The final payment is trimmed or topped up to clear the balance exactly, so it rarely equals the others — here it is $860.70, four cents over.
• Term accepts 1 to 600 months and the rate 0 to 100%. Signed in, five saved calculations are free and further ones cost 100 SMO each.

Frequently asked questions