Mortgage Calculator: How to Estimate Your Monthly Payment Like a Pro
Before you step into a bank or click 'apply', you need one number: the monthly payment. It decides which home you can afford, how much you can borrow, and how much interest you will hand over across 15, 20 or 30 years. This guide explains the payment formula in plain language, shows how the big three levers (loan size, rate, term) change your payment, and hands you a free mortgage calculator that does the math in seconds.
The Mortgage Payment Formula, Explained Simply
Lenders use an amortization formula: M = P × r(1+r)ⁿ ÷ ((1+r)ⁿ − 1), where P is the loan amount, r is the monthly interest rate (annual rate ÷ 12), and n is the number of monthly payments. Every payment first covers the interest owed that month, then pays down the principal.
You never need to touch this formula — our mortgage calculator computes the monthly payment, total interest and total cost instantly, and accepts an optional down payment.
15-Year vs 30-Year Mortgage: The Trade-Off
| 15-year | 30-year | |
|---|---|---|
| Monthly payment | Higher | Lower |
| Total interest | Much lower | Much higher |
| Home equity builds | Faster | Slower |
| Best for | Max savings | Max affordability |
A $250,000 loan at 6% costs about $2,110/month for 15 years (≈ $129,800 total interest) versus about $1,499/month for 30 years (≈ $289,600 total interest). Same loan, very different lifetime cost.
How the Down Payment Changes Everything
A larger down payment shrinks the principal, which lowers both the monthly payment and the interest charged over the life of the loan. A 20% down payment also usually removes private mortgage insurance — a meaningful monthly saving on top.
How Much House Can You Afford? The 28/36 Rule
Most lenders cap housing costs at about 28% of gross income and total debts at 36%. If you earn $6,000/month, a $1,680 monthly payment is the typical ceiling. Estimate your loan with the calculator, then add property tax and insurance for the real budget.
Five Questions to Ask Before You Apply
- Is the rate fixed or adjustable — and for how long?
- Are there prepayment penalties if I pay early?
- What are closing costs, and can they be rolled in?
- Does the advertised rate require points?
- What happens to my payment when taxes or insurance rise?
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Frequently Asked Questions
Use the amortization formula with your loan amount, monthly rate (annual ÷ 12) and number of months — or simply use our free mortgage calculator.
No — it covers principal and interest. Add property tax and insurance separately for your real budget.
Rates change constantly with the market. Compare current 15- and 30-year offers from several lenders and check your credit score first.
It depends: 15-year saves tens of thousands in interest but raises the monthly payment; 30-year is more affordable monthly but far more expensive overall.