Loan repayment calculator — equal payment & equal principal table
Simulate mortgage, auto, and student-loan repayments under both equal-payment and equal-principal schedules. Enter principal, annual rate, and term to see the monthly payment, total interest, total paid, and a full amortization table. Everything runs in your browser — no loan or income data is uploaded.
How to use
Pick a repayment mode (equal payment or equal principal), enter the principal, annual rate, and term (years + months), then press Calculate. The tool shows the monthly payment, total amount paid, and total interest, plus an amortization schedule you can toggle and download as CSV. The Sample button fills in a typical Japanese mortgage scenario (¥30M @ 1.5% / 35 years). All values stay on your device — nothing is uploaded.
FAQ
- Is the loan amount uploaded?
- No. Principal, rate, and term are all processed by JavaScript in your browser; nothing leaves your device. Safe to use for pre-approval and budgeting scenarios.
- Which repayment mode should I pick?
- Equal payment (元利均等) gives you a flat monthly amount — easier to budget and the dominant style for Japanese mortgages. Equal principal (元金均等) starts with the largest payment and shrinks each month; pays less total interest but requires more cash up front.
- What is the monthly payment formula?
- Equal payment: M = P × i × (1+i)^n / ((1+i)^n − 1), where P is principal, i = annual rate / 12, n = months. Equal principal: monthly principal = P / n; interest each month = remaining balance × i; payment = principal + interest.
- Are bonus payments supported?
- No. The tool models monthly-only repayments. For a Japanese bonus-and-monthly mix, split the principal into a bonus portion and a monthly portion and run the tool twice.
- Can I simulate prepayments?
- Not in this version. Export the amortization CSV and run a prepayment scenario in Excel / Google Sheets for now.
- The amortization table scrolls slowly
- A 35-year mortgage is 420 rows. The table is a plain HTML table (no virtualization), which is fine up to a few thousand rows. For heavy analysis, prefer the CSV export.
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