Calculator inputs
Example data table
| Scenario | Principal | APR | Term | Frequency | Extra | Scheduled Payment | Total Interest | Total Repaid | Actual Payments |
|---|---|---|---|---|---|---|---|---|---|
| Personal loan | $20,000.00 | 7.50% | 5 years | Monthly | $0.00 | $400.76 | $4,045.54 | $24,045.54 | 60 |
| Mortgage with extra | $250,000.00 | 5.20% | 30 years | Biweekly | $50.00 | $632.85 | $199,750.05 | $449,750.05 | 659 |
| Auto loan | $35,000.00 | 4.90% | 6 years | Monthly | $25.00 | $562.05 | $5,191.08 | $40,191.08 | 69 |
Formula used
Effective annual rate:
EAR = (1 + APR / c)c - 1
Here, c is the number of compounding periods in one year.
Periodic loan rate:
r = (1 + EAR)1 / p - 1
Here, p is the number of payment periods in one year.
Scheduled payment:
Payment = P × r / (1 - (1 + r)-n)
Here, P is principal and n is the planned number of payments.
Total loan interest:
Total Interest = Sum of all interest portions in the amortization schedule
Each period uses: Interest = Current Balance × Periodic Rate, and Principal Paid = Payment - Interest.
How to use this calculator
- Enter the original loan principal and annual interest rate.
- Add the full loan term using years and additional months.
- Choose how often you pay and how interest compounds.
- Add any extra amount you plan to pay every period.
- Set the first payment date to estimate the payoff date.
- Click the calculate button to show totals above the form.
- Review the summary cards and the full amortization schedule.
- Use the CSV or PDF buttons to export your results.
Frequently asked questions
1) What does total loan interest mean?
It is the sum of every interest charge paid across the full repayment schedule. It excludes the original principal because principal is money you borrowed, not a borrowing cost.
2) Does a higher payment frequency change the result?
Yes. Weekly or biweekly payments can reduce interest if balances fall sooner. The calculator converts the annual rate into a matching periodic rate before building the schedule.
3) How do extra payments help?
Extra payments reduce principal faster. That lowers future interest charges, shortens payoff time, and often creates noticeable savings over long loan terms.
4) Why are compounding and payment frequency separate?
Some loans compound monthly but accept payments biweekly or weekly. Keeping them separate makes the estimate more realistic for loans that do not align perfectly.
5) What happens when the rate is zero?
The calculator divides principal evenly across the planned payments. Total interest becomes zero, and total repaid matches the original amount borrowed.
6) Why can the last payment be smaller?
The final payment only needs to clear the remaining balance plus the last interest charge. If earlier payments reduce the loan faster, the last one may shrink.
7) Are fees included in the calculation?
No. This tool focuses on principal, interest, term, frequency, and extra payments. Origination fees, insurance, penalties, and taxes should be reviewed separately.
8) Can I use this for mortgages, personal loans, and auto loans?
Yes. It works best for fixed-rate amortizing loans. For variable-rate loans, recalculate whenever the interest rate or repayment structure changes.