Mortgage Acceleration Calculator
How to Use This Calculator
- 1
Enter the loan details
Fill in Loan Amount, Interest Rate, and Loan Term using the original principal, annual rate, and original term.
- 2
Add payment history and extra principal
Enter Months Already Paid, or leave it at 0 for a new loan, and enter Extra Monthly Payment. The calculator applies the extra amount to the regular monthly payment.
- 3
Compare the payoff results
Review Interest Saved, Time Saved, Accelerated Payment, and Remaining Balance, then compare the normal and accelerated balance paths in the chart and table.
Example Calculation
A borrower starts a $300,000, 30-year mortgage at 6.5% and adds $300 to each monthly payment from the beginning.
Loan Amount ($)
300,000
Interest Rate (%)
6.5
Loan Term (years)
30
Months Already Paid (months)
0
Extra Monthly Payment ($)
300
Results
Interest Saved
$135,115.62
Time Saved
9y 2m
Accelerated Payment
$2,196.20
Remaining Balance
$300,000.00. Insights chart and table compare the normal and accelerated balance and interest paths by year.
Tips
The $300 extra payment raises the monthly principal-and-interest payment to about $2,196
Try $150 and $500 in Extra Monthly Payment to compare the tradeoff between a manageable monthly increase and a faster payoff.
Starting extra payments later reduces the time available for savings
Change Months Already Paid to 60 while keeping the other inputs fixed. The calculator starts both payoff comparisons from the balance after those 60 scheduled payments.
A lump sum is different from a recurring extra payment
This calculator repeats Extra Monthly Payment every month. For a one-time principal reduction, compare a lump-sum scenario with the [additional principal payment mortgage calculator](/calculators/additional-principal-payment-mortgage-calculator/).
What this calculator estimates
Mortgage acceleration means paying more than the scheduled principal-and-interest amount to reduce the loan balance faster. This calculator compares projected interest and payoff time with and without a recurring extra monthly payment; it does not include escrow, fees, or changes in interest rates.
How the calculation works
For a fixed-rate loan, the scheduled monthly payment is calculated first:
M = P × r × (1 + r)^n / ((1 + r)^n − 1)
P is the original principal, r is the monthly interest rate (annual rate ÷ 12), n is the total number of monthly payments, and M is the scheduled monthly principal-and-interest payment. Each month, interest equals the current balance multiplied by r; the remainder of the payment reduces principal.
The accelerated path uses M plus the extra payment. For the example, the monthly rate is 0.065 ÷ 12 = 0.0054167 and the term is 30 × 12 = 360 payments. The standard payment is about $1,896.20; adding $300 makes the modeled payment about $2,196.20. The calculator simulates both paths month by month, including a smaller final payment when the remaining balance is less than the regular payment.
How the extra amount changes the payoff
The table shows the calculator’s approximate comparison for the same $300,000 loan at 6.5%, starting with no payments made. Values are rounded for display.
| Extra per month | Total monthly P&I payment | Approximate payoff time | Approximate interest saved |
|---|---|---|---|
| $0 | $1,896.20 | 30 years | $0 |
| $150 | $2,046.20 | About 24 years | About $90,000 |
| $300 | $2,196.20 | About 20 years 10 months | About $135,116 |
| $500 | $2,396.20 | About 17 years 10 months | About $185,000 |
The exact result depends on the entered loan balance, rate, term, and payment history. A higher extra payment saves more interest but also commits more cash each month. Before accelerating payments, compare that benefit with maintaining an emergency reserve, paying down higher-rate debt, and any employer retirement match you would otherwise miss.
If the mortgage has a variable rate, the estimate does not model future resets. Use an adjustable-rate mortgage calculator for rate changes, or a mortgage calculator to estimate the regular payment and housing costs. For a side-by-side comparison of loan offers, use the mortgage loan comparison calculator.
What to check before paying extra
Confirm that your servicer applies additional money to principal rather than advancing the next due date. Check for prepayment penalties and retain a record of how the payment was applied. The CFPB’s mortgage resources explain common loan-servicing and mortgage decisions, but your loan documents determine the terms of your specific loan.
When to use a different calculator
- Estimate the scheduled payment with taxes and insurance → mortgage calculator
- Compare two mortgage offers → mortgage loan comparison calculator
- Model an extra payment that changes the loan schedule → additional principal payment mortgage calculator
- Evaluate mortgage insurance costs → mortgage insurance calculator
Frequently Asked Questions
How do extra mortgage payments reduce interest?
An extra principal payment lowers the balance used to calculate interest in later months. Because the balance falls faster, less interest accrues over the remaining term, assuming the lender applies the extra amount to principal.
Does the calculator include payments I already made in Interest Saved?
No. It calculates interest saved by comparing two payoff paths from the remaining balance, so interest paid before Months Already Paid is excluded. Entering prior payments establishes the current modeled balance; it does not recalculate past interest savings.
Should I pay extra on my mortgage or keep the money in savings?
Keep enough liquid cash for emergencies and near-term costs before committing extra money to a mortgage. Extra principal can reduce future interest, but it is generally harder to access again than cash in a savings account; compare the mortgage’s effective cost with the value of liquidity and other high-interest debt.
Can my lender charge a fee for paying off my mortgage early?
Some loans have prepayment penalties, so check your note and closing documents before increasing payments or refinancing. The CFPB explains mortgage prepayment penalties and what to check.
Does the accelerated payment include taxes, insurance, or mortgage insurance?
No. It is the scheduled principal-and-interest payment plus Extra Monthly Payment. Property taxes, homeowners insurance, mortgage insurance, escrow changes, and fees are not modeled.