Calculator Inputs
Example Data Table
| Scenario | Loan Amount | Rate | Term | Monthly Extra | Annual Extra | Lump Sum |
|---|---|---|---|---|---|---|
| Starter plan | $250,000 | 6.25% | 30 years | $100 | $0 | $0 |
| Balanced plan | $320,000 | 5.85% | 25 years | $200 | $1,500 each December | $5,000 in month 24 |
| Aggressive plan | $450,000 | 6.75% | 30 years | $400 | $3,000 each June | $10,000 in month 12 |
Use the sample patterns above to test how recurring and one-time overpayments affect payoff timing and lifetime interest.
Formula Used
1) Standard mortgage payment formula
M = P × r ÷ (1 − (1 + r)−n)
M is the regular monthly payment, P is the loan principal, r is the monthly interest rate, and n is the total number of monthly payments.
2) Monthly interest
Interest = Current Balance × Monthly Rate
3) Principal paid
Principal Paid = Total Payment − Interest
4) Closing balance
Closing Balance = Opening Balance − Principal Paid
Overpayments are added on top of the regular payment, then applied directly toward principal. This reduces future interest and shortens the payoff period.
How to Use This Calculator
- Enter your mortgage amount, annual rate, and original term.
- Choose the mortgage start date and optionally enter your current regular payment.
- Add monthly overpayments, annual overpayments, or a one-time lump sum.
- Choose when overpayments begin and when they stop.
- Submit the form to see interest savings, term reduction, payoff dates, and the full amortization table.
- Use the CSV and PDF buttons to export the schedule for planning, sharing, or recordkeeping.
FAQs
1) What does a mortgage overpayment mean?
A mortgage overpayment is any amount you pay above the required regular installment. The extra money reduces principal immediately, which lowers future interest and can shorten the loan term.
2) Is monthly overpayment better than a lump sum?
Monthly overpayments usually reduce interest sooner because principal drops earlier every month. Lump sums can still be powerful, especially after bonuses, asset sales, or yearly savings targets.
3) Why is my regular payment adjusted upward?
If your entered regular payment is below the minimum needed to fully amortize the mortgage, the calculator raises it to the required minimum. This avoids negative amortization.
4) Does this calculator include taxes and insurance?
No. The calculation focuses on principal, interest, and extra payments only. Property tax, insurance, HOA, and escrow costs are not added to the amortization schedule.
5) Can I stop monthly overpayments after a few years?
Yes. Set the monthly overpayment end month to any value greater than zero. The calculator will stop applying recurring extra payments after that month.
6) What is the annual overpayment month used for?
It defines the calendar month when the annual extra payment is applied each year. This helps model strategies such as year-end bonuses or seasonal income surpluses.
7) Can this help compare different payoff strategies?
Yes. You can test combinations of monthly extras, annual extras, and lump sums. Then compare the resulting loan duration, interest cost, and payoff date.
8) Should I always overpay my mortgage?
Not always. Overpaying can save interest, but you should also consider emergency savings, higher-interest debt, investment goals, and any lender overpayment limits or penalties.