Mortgage Calculator
Supports commercial and housing fund loans with equal installment or equal principal
Mortgage Calculator
Mortgage Calculator Guide
Use this tool to estimate your monthly mortgage payment, total interest, and full repayment schedule. It supports both equal-installment (equal monthly payment) and equal-principal (fixed principal, declining interest) methods, with a pie chart showing how much of your payment goes to principal versus interest. Every calculation runs locally in your browser, so the loan amount and rate you enter are never uploaded to any server.
The Four Factors That Move Your Payment
Your monthly payment is set by loan amount, interest rate, loan term, and repayment method. Bigger loans, higher rates, and longer terms all raise both the monthly payment and the total interest. With the same principal, equal-principal costs less total interest than equal-installment, but its early payments are higher. Within your means, a larger down payment and a shorter term are the two levers that cut the most cost — use the calculator to line up several scenarios side by side.
Monthly Payment by Loan Size and Rate (30-Year Equal Installment)
Note: 3.5% is the current 5-year LPR (Sep 2026); 3.85% / 4.2% are historical high rates, shown for comparison only.
The table below is computed from the standard amortization formula (monthly rate = annual rate ÷ 12; payment = principal × rate × (1 + rate)^n ÷ [(1 + rate)^n − 1]) so you can locate your own range at a glance.
| Loan amount | 3.1% | 3.5% | 3.85% | 4.2% |
|---|---|---|---|---|
| ¥1,000,000 | ¥4,270 | ¥4,490 | ¥4,688 | ¥4,890 |
| ¥2,000,000 | ¥8,540 | ¥8,981 | ¥9,376 | ¥9,780 |
| ¥3,000,000 | ¥12,810 | ¥13,471 | ¥14,064 | ¥14,671 |
The pattern is steep: lifting the rate from 3.1% to 4.2% adds about ¥620 to the monthly payment on a ¥1,000,000 loan and roughly ¥220,000 of extra total interest over 30 years. Every 0.25-point move in the rate has an outsized lever on long-run cost.
Equal Installment vs Equal Principal: How Much Interest Differs?
For the same ¥1,000,000 over 30 years, equal-principal starts high and steps down each month (its last payment approaches the flat principal portion), while equal-installment stays fixed. The table shows both.
| Rate | Equal-installment monthly | Equal-principal first month | Equal-principal last month | Equal-principal total interest |
|---|---|---|---|---|
| 3.1% | ¥4,270 | ¥5,361 | ¥5,354 | ¥466,292 |
| 3.5% | ¥4,490 | ¥5,694 | ¥5,686 | ¥526,458 |
| 3.85% | ¥4,688 | ¥5,986 | ¥5,977 | ¥579,104 |
| 4.2% | ¥4,890 | ¥6,278 | ¥6,268 | ¥631,750 |
At 3.5%, equal-principal saves about ¥90,100 in total interest versus equal-installment (¥526,458 vs ¥616,561), but its first five years cost roughly ¥1,200 more per month. That is the core trade-off: "less interest" versus "lighter early load."
Three Worked Examples
- ¥1,000,000, 3.5%, 30 years, equal installment: monthly payment ¥4,490, total interest about ¥616,561, total paid ¥1,616,561.
- ¥2,000,000, 3.5%, 30 years, equal principal: first month ¥11,389, last month about ¥11,373 (principal portion ¥5,555.56, shrinking by roughly ¥15.4 per month), total interest about ¥1,052,917.
- ¥1,000,000, 3.5%, 20 vs 30 years: at 20 years the monthly payment is ¥5,800 with total interest ¥391,903; stretch to 30 years and the payment drops to ¥4,490 but total interest rises to ¥616,561 — ten extra years cut the monthly bill by ¥1,310 yet cost ¥224,658 more in interest.
If you plan to prepay, the interest can fall further: on the ¥1,000,000 / 3.5% / 30-year loan above, a one-time ¥500,000 payoff at the end of year 5 leaves a balance of about ¥896,971; after the payoff the remaining ¥396,971 refinanced over 25 years drops the monthly payment to about ¥1,987. Extra payments compound into real savings, which you can explore with our compound interest calculator.
About Mortgage Calculator
Mortgage Calculator is a completely free online tool that handles both equal-installment and equal-principal repayment, and works for commercial loans, housing-fund loans, or a combination of the two. Whether you are a casual user or a professional, you can run it instantly without installing any software.
Whether you are a first-time buyer, upgrading your home, or comparing mortgage plans, you can quickly see monthly payments and interest details. When you weigh the long-run cost, remember that extra payments behave like an investment: our compound interest calculator shows how money saved on interest could grow if invested instead, while the 2026 tax calculator can estimate the deduction side of mortgage interest.
How to Use
- Enter the total loan amount in the first field (units of 10,000).
- Enter the annual interest rate (%) and the loan term (years).
- Choose a repayment method: equal payment or equal principal.
- Click "Calculate" to see monthly payment, total interest, and a principal-interest chart.
Mortgage Calculator FAQ
Equal installment vs equal principal — how much total interest differs?
For ¥1,000,000 at 3.5% over 30 years: equal installment fixes the monthly payment at ¥4,490 with ¥616,561 of total interest; equal principal starts at ¥5,694 and steps down, with ¥526,458 of total interest. The gap is about ¥90,100, bought by carrying roughly ¥1,200 more per month in the first five years. Which you pick depends on whether you can absorb the heavier early load.
How much does each 0.25% rate cut save on the monthly payment?
On a ¥1,000,000 loan over 30 years, the current 5-year LPR of 3.5% gives a ¥4,490 monthly payment and about ¥616,561 of total interest; if the rate rose to 3.85% (a recent high), the payment climbs to ¥4,688 and total interest to ¥687,710. That 0.35-point gap alone adds roughly ¥71,000 of interest over 30 years — improving your credit to qualify for a lower rate, or choosing a lower rate quote, has a large effect on lifetime cost — convert the change with the percentage calculator if you want it as basis points.
Is a 30-year loan really better than a 20-year loan?
Not always. Thirty years eases the monthly load (¥1,000,000 at 3.5%: ¥4,490 over 30 years versus ¥5,800 over 20), but total interest jumps from ¥391,903 to ¥616,561 — an extra ¥224,658. If the money you free up earns more than your mortgage rate, the longer term can make sense; if not, a shorter term saves real money. Match the term to your cash flow and your other returns.
Prepayment: shorten the term or reduce the payment?
For the same lump sum, shortening the term saves more interest than reducing the monthly payment, because the principal drops earlier and the interest base falls faster. If your monthly load is comfortable, choose "shorten term"; if you need immediate relief on the bill, choose "reduce payment." Use the date calculator to count down to your target prepayment date.
Can housing-fund and commercial loans be combined?
Yes — that is a "combination loan." The housing-fund portion has a capped limit and a lower rate, and the remainder is covered by a commercial loan, so the blended rate is below a pure commercial loan. Compute the housing-fund part first, then run the commercial portion at the commercial rate here; add the two monthly payments for the total.
How does the down-payment ratio affect the monthly payment?
A higher down payment lowers the principal, so both the monthly payment and total interest shrink. On a ¥3,000,000 home: a 30% down payment (¥2,100,000 loan) costs about ¥9,430 per month at 3.5% over 30 years, while a 40% down payment (¥1,800,000 loan) costs about ¥8,083 — about ¥1,347 less each month and roughly ¥185,000 less total interest. Raising the down payment is the most direct way to cut the monthly bill.
Equal Installment vs Equal Principal — Which Saves More Interest?
The two mainstream repayment methods suit different people. Equal installment keeps the monthly amount fixed: you pay more interest and less principal early on, but the payment is predictable and easy to budget, which fits stable salaries. Equal principal repays the same principal slice every month, so the interest shrinks and the payment falls over time; total interest is lower, but the early payments are heavier, which suits borrowers with stronger upfront cash flow who want to minimize total cost. The difference is purely the pace at which you repay principal early — and that pace decides the final interest bill.
In short: if you want a fixed, knowable monthly number, choose equal installment; if you can carry higher early payments and want to save the most interest, choose equal principal. Neither is wrong — it depends on your income shape and long-term plan.
Hidden Costs Home Buyers Often Overlook
Many buyers count only the monthly payment and miss a stack of extra outlays. Beyond the down payment and the mortgage, buying a home usually involves deed tax, stamp duty, a maintenance fund, loan fees, agent commissions, and insurance, plus renovation, appliances, and ongoing property costs. Added together these are far from trivial, and skipping them leads to the classic "can afford the house but not the extras" trap. Whether the rate is floating or fixed, and whether a housing-fund or combination loan applies, also moves the long-run interest cost and is worth checking before you sign.
Total cost of ownership — monthly payment plus one-time taxes plus holding costs — should drive your budget and loan plan far more than the headline "how much can I borrow." If you are also planning other big numbers, the compound interest calculator helps you compare paying down the loan against investing the cash.
How Should You Read the Result?
The monthly payment, total interest, and principal-versus-interest chart let you see at a glance how much of each payment is interest, and how much interest you will pay overall. Use them to check the payment fits your repayment capacity (commonly kept below a sensible share of monthly income), to compare rate and term scenarios, and to decide whether a combination loan or prepayment is worth it. For a broader comparison, pair this tool with the housing-fund and loan-comparison calculators referenced near the top of the page.