Mortgage Calculator

What is a mortgage calculator?#

A mortgage (or installment loan) calculator turns four numbers — how much you borrow, the interest rate, how many years, and the repayment method — into the one number every borrower actually wants: the monthly payment, plus the painful truth of how much interest you pay over the whole term. It works from the standard amortization formula, the same one banks use to print your repayment schedule.

This page supports the two repayment methods common for home loans. Equal-payment (also called equal-installment) keeps the monthly payment flat for the whole term — interest is front-loaded, so early payments are almost all interest and the principal barely moves at first. Equal-principal keeps the principal slice flat instead, so the payment starts higher and declines every month as interest is charged on a shrinking balance. The tool lays out the full month-by-month schedule so you can see exactly where every yuan, dollar or euro goes.

How to use it#

1. Enter the Principal — the amount you are borrowing, before any down payment. The box is plain currency units, no symbol.
2. Enter the nominal annual interest Rate (%) — for example 4.9 for 4.9%. If your bank quotes it, use the quoted nominal rate; the tool converts it to a monthly rate internally.
3. Enter the loan term in Years (whole years; the tool multiplies by 12).
4. Pick the Method from the dropdown: equal-payment (flat monthly) or equal-principal (declining monthly).
5. Click Compute. The summary bar shows the monthly payment (for equal-principal this is the first month’s payment, the highest), the total paid across the whole term, the total interest, and the number of months.
6. Expand Schedule to scroll every month: payment, principal portion, interest portion, and remaining balance — useful for seeing when the principal finally starts dropping fast, or for planning an early payoff.

Key features#

• Both common repayment methods, computed from the exact amortization formula — no approximation, no spreadsheet.
• Full month-by-month schedule in a scrollable table, so you can answer “how much principal is left after month 84?” without redoing the math.
• Honest totals. Total interest is shown next to total paid, because the gap between them is the real cost of a long loan.
• Rounded to the cent on every row, with the final payment settling rounding dust so the balance ends at exactly zero.
• 100% local. Your numbers stay in the browser — this is the kind of figure you do not want uploaded anywhere.

Worked example#

A 1,000,000 home loan at 4.9% annual over 30 years. With equal-payment selected and Compute clicked:

So a 30-year loan at 4.9% nearly doubles the cost — you pay back about 1.91 for every 1 borrowed. Open the schedule and look at month 1: of the 5,307.27 you pay, only about 1,224 is principal and the remaining 4,083 is interest. By month 360 the split has reversed — almost all principal. That is what “interest is front-loaded” means in practice.

Now switch the dropdown to equal-principal and recompute. The first payment jumps to about 6,861 (because the flat principal slice of 2,777.78 plus 4,083 first-month interest is heavier than the equal-payment figure), but it declines every month. The last payment is about 2,791, and the total interest falls to roughly 737,000 — around 173,000 less than equal-payment. The trade-off is real: equal-principal costs less overall but demands more cash early on.

FAQ#

Which method pays less interest?#

Equal-principal always wins on total interest, because you are paying down principal faster from month one — so interest is charged on a smaller balance every month. The catch is the early payments are higher, which strains cash flow at exactly the time many buyers are also furnishing the home. Equal-payment trades a higher lifetime cost for a flat, predictable monthly burden.

Why is so much of my early payment just interest?#

Each month the bank charges interest on the remaining balance. Early on almost the whole principal is still outstanding, so the interest portion is large; the fixed payment can only cover a sliver of principal. As the balance falls, the interest portion falls too, freeing more of the same payment for principal — a snowball that accelerates toward the end of the term.

Does this include fees, insurance, or prepayment penalties?#

No. The tool computes pure amortization from principal, rate and term. Real-world closing costs, mortgage insurance, property tax, and any early-repayment penalty are extra and vary by lender — add them on separately when comparing loan offers.

Why does the total interest look so high for 30 years?#

Because interest compounds on a balance that is being paid down slowly. Stretching the same principal over more years lowers the monthly payment but keeps the balance outstanding for longer, so interest accrues for longer. Halving the term often cuts total interest far more than people expect — try changing Years from 30 to 15 and watch the total interest column.