Amortization Schedule Calculator

How amortization works

On an amortizing loan the payment is fixed, but what that payment does changes every single month. The lender charges interest on the balance you still owe, so the interest share is at its largest on day one and shrinks as the balance comes down. The principal share grows by exactly the same amount, which keeps the total payment level.

Take a $250,000 loan at 6.50% over 30 years. The payment is $1,580.17 a month. Of the very first one, $1,354.17 is interest and only $226.00 touches the debt. Across the whole first year you hand over $18,962 and reduce the balance by $2,794 — under 15% of what you paid.

The two halves don't cross over until payment 233, more than nineteen years in. By the final payment you'll have paid $568,861 for the $250,000 you borrowed, of which $318,861 is interest.

The amortization formula

The fixed payment comes from one equation:

M = P × (r(1+r)ⁿ) / ((1+r)ⁿ − 1)

where P is the principal, r is the interest rate per period (the annual rate divided by 12 for a monthly loan) and n is the total number of payments.

For the loan above: P = 250,000, r = 0.065 / 12 = 0.00541667, n = 30 × 12 = 360. That gives (1+r)ⁿ = 6.991798, so M = 250,000 × 0.00541667 × 6.991798 / 5.991798 = $1,580.17.

You will often see the same formula written as M = P × r / (1 − (1+r)⁻ⁿ) — it is algebraically identical, just divided through by (1+r)ⁿ. In Excel or Google Sheets, =PMT(6.5%/12, 360, -250000) returns the same $1,580.17, and IPMT and PPMT give the interest and principal parts of any single payment; our amortization schedule Excel template is built on exactly these functions.

The schedule itself is then just three steps repeated once per payment:

1. Interest = current balance × r
2. Principal = M − interest
3. New balance = current balance − principal

Repeat until the balance reaches zero. That is all an amortization calculator does — the work is in doing it 360 times without an arithmetic slip. Our rounding rules and every assumption behind the mortgage, PMI and payoff figures are on how we calculate.

How to read your amortization schedule

Every row is one payment, split into what the lender keeps and what actually reduces your debt:

Payment	Date	Interest	Principal	Balance
1	Jan 2026	$1,354.17	$226.00	$249,774.00
2	Feb 2026	$1,352.94	$227.23	$249,546.77
3	Mar 2026	$1,351.71	$228.46	$249,318.31
233	May 2045	$788.75	$791.42	$144,824.47
360	Dec 2055	$8.51	$1,571.66	$0.00

Three things are worth noticing. The payment never changes. The interest column falls slowly at first and then faster, because it tracks a balance that is itself falling faster and faster. And at payment 233 — the crossover — principal finally overtakes interest, yet you still owe $144,824, well over half the original loan, despite being nearly two-thirds of the way through the term.

That asymmetry is why selling or refinancing early costs more than people expect: the equity you have built is much smaller than the fraction of payments you have made. Before you refinance, run the new loan through a mortgage refinance calculator to see whether the lower rate outweighs restarting the clock.

10, 15, 20 and 30-year amortization compared

The term changes the schedule more than any other input. Here is the same $250,000 loan at 6.50% amortized over four common terms:

Term	Payment	Total interest	Owed after 5 years	Principal > interest from
10 years	$2,838.70	$90,643.93	$145,082	the first payment
15 years	$2,177.77	$141,998.31	$191,793	year 5
20 years	$1,863.93	$197,343.88	$213,973	year 10
30 years	$1,580.17	$318,861.22	$234,027	year 20

A 30-year amortization schedule buys the lowest payment at the price of more than three times the interest of a 10-year one, and after five years of payments you still owe over 93% of the loan. Run the calculator above with your own term to see the full payment-by-payment table for it.

What extra payments really save

Anything you pay above the required amount goes straight to principal, which permanently shrinks the base that all future interest is charged on. The effect compounds, so it is far larger than the extra money itself.

On the same $250,000 loan at 6.50%:

• $100 extra a month clears the loan in 304 payments instead of 360 — four years and eight months early — and saves $58,860 in interest.
• $200 extra a month clears it in 265 payments, nearly eight years early, saving $97,618.

The mortgage payoff calculator does this arithmetic on your own balance: enter what is left, the rate and the term still to run, and it returns the new payoff date and the interest that never gets charged. For a full amortization schedule with extra payments, open the advanced options on the mortgage calculator or any loan calculator and enter an Extra Payment: the table is rebuilt with the extra amount applied every month.

Two practical cautions. Check your loan agreement for prepayment penalties first — they are rare on mortgages but common on some auto and personal loans. And tell the servicer in writing that extra money is to be applied to principal, not held as a prepaid future installment, which is the default at some lenders.

Loans that don't amortize the way you expect

Not every loan follows a clean amortization schedule:

• Interest-only loans charge only the interest for an initial period, so the balance doesn't move at all until the full payment kicks in.
• Balloon loans are amortized over a longer schedule than their actual term, leaving a large lump sum due at the end.
• Negative amortization happens when the payment is smaller than the interest due; the shortfall is added to the balance and your debt grows even though you are paying.
• Adjustable-rate loans re-cut the schedule at every rate reset, so any schedule you build is only valid until the next adjustment.
• Credit cards have no fixed end date at all — the minimum payment is a percentage of the balance, so it falls as the balance falls and the payoff stretches out.