How to use the extra payment calculator
Prepare the values for this calculation
Estimate payoff time and modeled interest savings from adding a monthly extra payment to a fixed-rate loan. Use the formula below to check that it answers your question. Read the input units before transferring figures from a statement, measurement or dataset.
Enter and check each input
- Remaining loan balance: enter a value at least 1e-06. Use the unit named in the label or selected above. Do not leave this required field blank.
- Annual interest rate (%): enter a value at least -99 and no more than 1000. Use the unit named in the label or selected above. Do not leave this required field blank.
- Remaining term (months): enter a value at least 1 and no more than 1200 and a whole number. Use the unit named in the label or selected above. Do not leave this required field blank.
- Extra monthly payment: enter a value at least 0. Use the unit named in the label or selected above. Do not leave this required field blank.
The input table gives a complete example. Keep units and time periods consistent across related fields.
Calculate and resolve any input error
Choose Calculate after entering the values. Changes also update the answer after a short pause. If an error appears, follow its message, correct the field and calculate again. Reset restores the example values.
Interpret the answer
Check Modeled payoff time first. With the unchanged example inputs, it is 191 months. Compare the additional metrics with the primary result; each has its own label and unit.
Compare and keep a useful result
For a controlled comparison, keep every other example input unchanged and change Remaining loan balance from 200000 to 220000. The resulting Modeled payoff time is 194 months. This illustrates the equation’s response to that input, rather than a forecast of real events.
Read the chart’s axis labels and data table. A scenario curve changes one stated input while holding the others fixed; it does not add external observations. Use Download graph to save an available chart as a PNG.
Use Copy result or Download CSV to keep the answer. Share tool shares the page address without placing your input values in the URL. Recheck inputs and assumptions before using the result for a decision.
Extra Payment Calculator formula
Simulates monthly interest and payment application using the standard amortizing required payment plus entered extra principal.
Inputs and units
| Input | Format / range | Example |
|---|---|---|
| Remaining loan balance | minimum 1e-06 | 200000 |
| Annual interest rate (%) | minimum -99; maximum 1000 | 6 |
| Remaining term (months) | minimum 1; maximum 1200; whole number | 240 |
| Extra monthly payment | minimum 0 | 200 |
Worked example
Using the example inputs above, the modeled payoff time is 191 months.
- Modeled payoff time
- 191 months
- Base required payment
- $1,432.86
- Modeled interest saved
- $33,576.10
Results and assumptions
The output uses the modeled payoff time convention and formula shown above. Match the entered units and source assumptions when comparing results.
Rates, fees and tax assumptions are entered values. This calculation does not quote a lender, determine a tax liability or guarantee an investment return.
Fix an input or unexpected result
Remaining loan balance is required. Enter remaining loan balance using the format and bounds in the input table. Zero and an empty field are different: use zero only if it is allowed and represents your data.
If your answer differs from the example, choose Reset and compare every field, including selected units and options. Check percentage versus decimal entry and whether values describe the same period. Round only the final displayed answer when reproducing the formula.
If a discrepancy remains, report the calculator issue with the page address, non-sensitive example inputs, actual result, expected result and a reference for your calculation.