Mortgage Calculator

How to Use

Enter the loan amount, loan term (in years), and annual interest rate (%). Your monthly payment, total payment, and total interest are calculated instantly as you type.

Switch between the "Equal Monthly Payment" and "Equal Principal Payment" tabs to compare both repayment methods under the same conditions. This makes it easy to see the trade-off between stable monthly payments and lower total interest.

The amortization table below the results shows the first 12 and last 12 payment periods. Click "Show all" to expand the full schedule. Use the "Copy Result" button to share the estimate via messaging apps or save it to your notes.

How the Calculation Works

Equal Monthly Payment (Fixed-rate amortization): The monthly payment M is calculated as M = P × r × (1+r)^n ÷ ((1+r)^n − 1), where P is the loan principal, r is the monthly interest rate (annual rate ÷ 12 ÷ 100), and n is the total number of payments (years × 12). In early payments, a larger share goes toward interest; over time, more goes toward principal.

Equal Principal Payment: Each month, a fixed amount of principal is repaid — calculated as floor(P ÷ n). The interest for each period is computed on the remaining balance, so payments start higher and gradually decrease. This method reduces total interest paid compared to the equal monthly payment method.

Key comparison — Equal Monthly vs. Equal Principal (example: $300,000 loan, 30 years, 4.0% rate): With equal monthly payment, you pay approximately $1,432 per month for all 360 payments, with total interest of approximately $115,500. With equal principal payment, your first payment is approximately $1,833, gradually decreasing to approximately $836 for the final payment, with total interest of approximately $90,900 — saving about $24,600 compared to equal monthly. The first-month difference is about $400. When income is unstable (e.g., during parental leave or career transitions), equal monthly payment is the more practical choice. Equal principal payment rewards borrowers with strong early cash flow by front-loading principal repayment.

Key insight — the cost of 0.1% in interest rate: On a $300,000 loan over 30 years, a rate of 4.0% vs. 4.1% shows a monthly payment difference of only about $18 — easy to overlook. But over 30 years (360 payments), that gap becomes approximately $6,400 in additional interest. Use this calculator to stress-test your budget: enter your current rate, then add 0.5% and 1.0% to see how higher rates would affect your monthly payment and total cost before committing to a variable-rate mortgage.

Frequently Asked Questions

Which method saves more money — equal payment or equal principal?

Equal principal payment results in lower total interest because the loan balance decreases faster, meaning less interest accrues over time. However, the initial monthly payments are higher than with equal monthly payment. Run the same loan details through both tabs on this calculator to see the exact difference for your situation.

Can I calculate payments with a balloon payment or bi-weekly schedule?

This calculator is designed for standard monthly repayment schedules without balloon payments. For bi-weekly payments or balloon structures, please use your lender's official loan calculator, as those repayment structures involve different compounding methods.

How do I estimate payments for a variable-rate mortgage?

Enter the current introductory rate to see your initial payments. Then run the same loan with rates 1–2% higher to stress-test your budget. If the higher-rate scenario is unaffordable, you may want to consider a shorter loan term or a fixed-rate product instead.

Why might my actual payment differ from this calculator's result?

This tool calculates principal and interest only. Your actual mortgage payment may also include property tax escrow, homeowner's insurance, private mortgage insurance (PMI), origination fees, or other lender charges. Rounding methods also vary slightly between institutions. Always confirm the exact payment schedule with your lender before signing.

Does this calculator support bonus payments or lump-sum repayments?

This calculator covers standard monthly repayment only, without any lump-sum bonus payments. If your loan includes periodic lump-sum payments, the actual total interest will be lower than shown here. For a more precise estimate that includes those payments, please use your lender's official loan simulator. Note that all results from this tool are estimates only.

Why might results differ from my lender's calculator?

Different lenders use slightly different methods for rounding monthly interest, handling the first payment date, or incorporating mortgage insurance premiums. This tool uses the standard annuity formula for estimates. For official figures, please consult your lender directly.

This tool provides estimates only. Actual mortgage payments may differ due to your lender's calculation method, fees, insurance, or other factors. Please consult your lender for official payment details.

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