Loan repayment and interest calculator
Model a fixed-rate monthly loan schedule, interest costs and extra principal payments. Compare the payoff time with the same loan without extras.
Inputs
Hypothetical example. Replace these inputs with your own.
Result
Calculation result
Example result
- Regular monthly payment
- 100 quote
- Total interest
- 0 quote
- Principal and interest paid
- 1,200 quote
- Separate upfront fee
- 0 quote
- Interest and upfront fee
- 0 quote
- Months until payoff
- 12 months
- Interest saved against no extras
- 0 quote
- Months saved against no extras
- 0 months
- This fixed monthly model divides the nominal annual rate by 12. The regular payment and each month's interest are rounded half up to whole cents; the regular payment is at least one cent.
- Monthly extras and lump sums reduce principal after that month's interest. Payments are capped at the amount owed, and the regular payment is not recast. Extra payments scheduled after payoff are unused.
- The upfront fee is paid separately at the start and is not financed. Principal and interest paid excludes that fee. Savings compare with the same cent-rounded schedule without any extras.
- The final contractual month clears any remaining balance. The schedule shows actual payments, including a smaller final payment or an adjustment caused by cent rounding.
- Daily accrual, changing rates, taxes, insurance, penalties and actual dates are excluded. The nominal rate is not a regulatory APR calculation.
| Month · month | Opening balance · quote | Rounded interest · quote | Regular payment paid · quote | Extra payment paid · quote | Principal repaid · quote | Total payment · quote | Closing balance · quote |
|---|---|---|---|---|---|---|---|
| 1 | 1,200 | 0 | 100 | 0 | 100 | 100 | 1,100 |
| 2 | 1,100 | 0 | 100 | 0 | 100 | 100 | 1,000 |
| 3 | 1,000 | 0 | 100 | 0 | 100 | 100 | 900 |
| 4 | 900 | 0 | 100 | 0 | 100 | 100 | 800 |
| 5 | 800 | 0 | 100 | 0 | 100 | 100 | 700 |
| 6 | 700 | 0 | 100 | 0 | 100 | 100 | 600 |
| 7 | 600 | 0 | 100 | 0 | 100 | 100 | 500 |
| 8 | 500 | 0 | 100 | 0 | 100 | 100 | 400 |
| 9 | 400 | 0 | 100 | 0 | 100 | 100 | 300 |
| 10 | 300 | 0 | 100 | 0 | 100 | 100 | 200 |
| 11 | 200 | 0 | 100 | 0 | 100 | 100 | 100 |
| 12 | 100 | 0 | 100 | 0 | 100 | 100 | 0 |
Saved scenarios
Save up to 20 new-tool scenarios on this device, separately from the six existing tools. Prices and balances stay out of the URL. DCA, journal and correlation scenarios save settings and a digest, requiring the matching CSV again to calculate.
Saving requires browser storage and Web Locks.
Formula and worked example
Monthly rate = nominal annual percent / 1,200. Payment uses the fixed monthly annuity formula, or principal / months at zero interest. Monthly interest and payments round to cents; the final contractual installment clears any residual.
Hypothetical loan: 1,200 at 0% over 12 months needs 100 each month. Adding 100 in extra principal each month pays it off in six months. This model excludes daily interest, variable rates, taxes, insurance and prepayment penalties.
These estimates use bounded decimal arithmetic. They are scenario calculations, not trading instructions or forecasts.
Methodology sources: CFPB loan principal and interest
Related tasks and reading
This website is developed by Zack White and Vincent Hale.