How to use the mortgage calculator
For most people a mortgage is the largest debt they will ever take on, and the repayment method you choose has a big effect on total interest paid. This tool works out the full numbers for both mainstream repayment methods, including the period-by-period breakdown, so you can decide.
Equal instalment vs equal principal
Equal instalment (annuity): the total payment each period never changes. Early on, interest makes up most of it and principal very little; over time the principal share climbs. The advantage is a fixed monthly payment, which makes cash flow easy to plan — good for salaried people with steady income. The drawback is that total interest is higher than with equal principal.
Equal principal: the principal repaid each period is fixed (loan amount ÷ number of periods), and interest is charged on the remaining balance, so the payment falls month by month. The advantage is lower total interest; the drawback is a heavy payment early on. It suits people with higher income, or who expect their income to decline.
The formulas are:
- Equal instalment payment =
principal × monthly rate × (1+monthly rate)^periods ÷ [(1+monthly rate)^periods - 1] - Equal principal: principal per period =
principal ÷ periods, interest in period n =remaining principal × monthly rate
Which one works out better
If you look only at total interest, equal principal saves more. On 1,000,000 over 30 years at 3.1%, the gap in total interest between the two is typically in the hundreds of thousands. But equal principal means a considerably larger payment early on. If that difference goes into another investment earning more than the mortgage rate, equal instalment isn't necessarily the loser.
Conversely, if you just want a smaller monthly payment and more cash on hand, equal instalment fits better. The real question isn't which one is "better value" — it's which one matches your cash flow and your ability to put money to work.
About the interest rate
Mortgage rates are set as a benchmark loan prime rate (LPR) plus or minus a spread. The 5-year-plus LPR is adjusted from time to time, and existing mortgages generally reset to the new LPR on their annual repricing date. This tool calculates at a fixed rate, which is suitable for estimating and side-by-side comparison — your actual repayment amounts are governed by your bank's contract.
Thinking about early repayment
Whether repaying early is worthwhile comes down to comparing the mortgage rate with what else your money could earn. At a 3.1% mortgage rate, if you can find a low-risk investment yielding a stable 4%+, the opportunity cost of repaying early is high. But note two things. First, once an equal-instalment loan is into its middle or later years, interest is a small share of the remaining balance, so repaying early saves little. Second, some banks charge a penalty for early repayment or restrict when it can be done.
Frequently asked questions
Why doesn't this match the bank's figure exactly?
Three common reasons. The bank charges interest by actual days, while this tool uses whole months. The bank may handle the first or last period irregularly. And a rate change mid-loan means interest is split across two rates. This tool's results are for estimating and comparison — the repayment schedule from your bank is authoritative.
How does a combined loan work?
Choose "combined loan" and enter the amounts and rates for the commercial loan and the housing provident fund loan separately; the tool calculates each and then totals them. Provident fund loans have a cap that varies by city, and anything above it can only go through a commercial loan — that is why combined loans exist.
Can I switch from equal principal to equal instalment partway through?
Generally yes, by applying to the bank. Some banks charge a fee or limit how often you may switch. After the change, everything is recalculated on the remaining principal and remaining periods. Rules differ by bank, so ask the branch handling your loan first.
Is my data uploaded?
No. Everything is calculated in your browser. The loan amount, rate and other details you enter never leave your device.