Estimate the monthly principal-and-interest payment on a mortgage, plus the total repaid and the total interest.
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A 300,000 home with 60,000 down leaves a 240,000 loan. At 5% over 30 years the payment is 1,288.37 a month, and the 360 payments carry 223,813.88 of interest. Choosing 15 years instead raises the payment to 1,897.90 but cuts interest to 101,622.85.
The financed principal is the price minus the down payment. A fixed-rate amortisation formula then spreads that principal over the number of monthly payments so that every payment is equal, with interest charged on the balance that is still outstanding.
The figure covers principal and interest only. Property tax, home insurance, mortgage insurance, service charges and closing costs are excluded and can add a substantial amount to the real monthly housing cost. It assumes a fixed rate for the whole term, so variable-rate loans will drift from this estimate.
Enter the property price, your down payment, the annual interest rate and the term. A 300,000 home with 60,000 down leaves a 240,000 loan. At 5% over 30 years the principal-and-interest payment is 1,288.37 a month, and total interest over 360 payments is 223,813.88. The payment excludes property tax, home insurance, mortgage insurance, service charges and closing costs, which can add a substantial amount to the real monthly housing cost.
Putting down 30,000 instead of 60,000 raises the loan to 270,000 and the payment to 1,449.42, an extra 161.05 a month, with 27,976.74 more interest over 30 years. A one-point higher rate matters even more: the same 240,000 at 6% costs 1,438.92 a month, 150.55 more, and adds 54,197.77 of interest. Compare quotes on both the rate and the fees, because a lower rate with large upfront charges may not be cheaper overall.
Choosing 15 years instead of 30 raises the payment on 240,000 at 5% to 1,897.90 but cuts total interest to 101,622.85, saving 122,191.03. The calculation assumes a fixed rate and equal payments. Variable-rate loans change over time, and in Japan many buyers compare variable rates with fixed products such as Flat 35: a 30,000,000 loan at 1.5% over 35 years costs 91,855.33 a month. This is an estimate, not an offer; lenders set the actual rate, fees and eligibility.
| Input | Result |
|---|---|
300,000 − 60,000 · 5% · 30 y | 1,288.37 × 360 · 240,000 |
300,000 − 30,000 · 5% · 30 y | 1,449.42 × 360 · 270,000 |
300,000 − 60,000 · 6% · 30 y | 1,438.92 × 360 · 240,000 |
300,000 − 60,000 · 5% · 15 y | 1,897.9 × 180 · 240,000 |
35,000,000 − 5,000,000 · 1.5% · 35 y | 91,855.33 × 420 · 30,000,000 |
Putting down 30,000 instead of 60,000 on the same 300,000 home raises the loan to 270,000 and the payment to 1,449.42, which is 161.05 more a month and 27,976.74 more interest over 30 years. A larger deposit may also remove mortgage insurance, which this estimate does not model.
More than most people expect. The same 240,000 at 6% instead of 5% costs 1,438.92 a month, 150.55 more, and adds 54,197.77 of interest across the term. Compare quotes on the rate and the fees together, because a lower rate with large upfront charges is not always cheaper overall.
It depends on whether the payment is comfortable. On 240,000 at 5%, moving from 30 years to 15 raises the monthly figure to 1,897.90 but saves 122,191.03 in interest. Fixed products elsewhere work the same way: a 30,000,000 loan at 1.5% over 35 years, like Japan’s Flat 35, costs 91,855.33 a month over 420 payments.