What does this tool do
The Loan Calculator helps you understand the cost of borrowing money. Enter the loan amount, interest rate, and term, and it computes your payment per period, total interest over the life of the loan, and a full payment schedule showing how each payment splits between principal and interest. It supports multiple loan types (amortizing, interest-only, balloon, simple interest), payment frequencies (monthly, bi-weekly, semi-monthly, weekly), optional down payments, and extra principal payments.
How to use it
- Enter the loan amount — The total amount you're borrowing (principal).
- Set the annual interest rate — As a percentage (e.g. 5 for 5% per year).
- Choose the term — Loan length in years (e.g. 30 for a 30-year mortgage).
- Add a down payment (optional) — If you're paying part upfront, enter it here. It reduces the principal before the first payment.
- Select loan type — Amortizing (standard), interest-only, balloon, or simple interest. Some types require additional inputs.
- Choose payment frequency — Monthly, bi-weekly, semi-monthly, or weekly.
- Add extra payments (optional) — Recurring extra per period or one-time lump sums to model early payoff.
- View results — The tool shows:
- Payment per period (or monthly payment when frequency is monthly)
- Total amount paid over the life of the loan
- Total interest paid
- Payment schedule with each payment's breakdown (copyable to clipboard)
- Interest saved and early payoff details when extra payments are used
How it works
Amortizing (default)
Uses the standard reducing-balance amortization formula:
PMT = P × [r(1+r)^n] / [(1+r)^n - 1]
Where:
- P = principal (loan amount minus down payment)
- r = interest rate per period (annual rate ÷ periods per year ÷ 100)
- n = total number of payments (years × periods per year)
For interest-free loans (0% rate), the payment per period is simply P / n.
Each period, interest is calculated on the remaining balance, and the rest of the payment goes toward principal.
Interest-only
Pay only interest for a specified number of years. After that, the remaining principal is amortized over the remaining term using the standard formula. Useful for mortgages with an interest-only introductory period.
Balloon
Lower periodic payments with a large lump sum (balloon) due at the end. The periodic payment is computed so that the balance reaches the balloon amount at term end. Final payment = regular payment + balloon.
Simple interest
Interest is calculated on the original principal for the full term (flat, not reducing balance). Total interest = P × (rate/100) × years; payment per period = (P + total interest) / n.
Payment frequency
| Frequency | Periods per year |
|---|---|
| Monthly | 12 |
| Bi-weekly | 26 |
| Semi-monthly | 24 |
| Weekly | 52 |
All calculations run entirely in your browser. No data is sent to any server.
Use cases & examples
- Mortgages — Estimate monthly payments and total cost for a home loan. Use bi-weekly frequency to model accelerated payoff.
- Auto loans — Compare financing options; some use simple interest.
- Personal loans — See how term and rate affect your payment.
- Interest-only mortgages — Model the interest-only phase and transition to amortizing.
- Balloon loans — Business or short-term loans with a balloon at maturity.
- Extra payments — See how recurring or one-time extra principal reduces total interest and shortens the term.
Example
A $300,000 loan at 5% for 30 years with no down payment (amortizing, monthly):
- Monthly payment: ~$1,610
- Total paid: ~$579,000
- Total interest: ~$279,000
Same loan with $200/month extra principal:
- Paid off in ~24 years
- Interest saved: ~$58,000
Limitations & known constraints
- Term cap — Maximum loan term is 50 years.
- Whole years only — Term must be a positive integer (no fractional years).
- No fees — Closing costs, origination fees, and insurance are not included.
- Fixed rate — Adjustable-rate mortgages (ARMs) are not modelled.