Baseline Monthly Payment
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Standard, fixed-rate payment.
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Inputs
Amount borrowed at origination.
Enter as percent (e.g., 6.75).
Whole years only.
How many monthly payments you have made.
Additional amount applied to principal each month.
Used to estimate payoff dates.
Results
New Monthly Outflow
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Baseline + extra principal.
Years Off Mortgage
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Months saved: —
Interest Saved
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Reduction vs. baseline: —
Original Payoff Date
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Assuming start month provided.
New Payoff Date
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With extra payments.
Amortization (Accelerated) 0 rows
| Month # | Payment | Interest | Principal | Extra | Balance |
|---|---|---|---|---|---|
| Run a calculation to see the schedule. | |||||
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How This Mortgage Calculator Works
This tool models a standard, fixed-rate, fully-amortizing mortgage. It computes your baseline monthly payment, advances the loan if you have already made payments, and then simulates an accelerated schedule by applying your extra principal every month.
- Baseline payment: P × r / (1 − (1 + r)−n) with r = APR/12 and n = years × 12.
- Order of operations: Monthly interest accrues on the current balance, the baseline principal is applied, then any extra principal (capped so the balance never goes negative).
- Results: You’ll see years and months saved, interest saved, and new payoff timing versus the original schedule.
- Privacy: Everything runs in your browser—no data leaves your device.
Frequently Asked Questions
What does the Years-Off Mortgage Calculator do?
It shows how adding monthly extra principal to a fixed-rate mortgage reduces your payoff time and total interest, including updated payoff dates when a start month is provided.
How is the monthly payment calculated?
Using the standard amortization formula P × r / (1 − (1 + r)−n) where r is the monthly rate (APR/12) and n is the number of months.
Does this handle variable or adjustable rates (ARM)?
No. This calculator models a fixed-rate, fully amortizing loan. For ARMs, rates and payments can change, which isn’t simulated here.
What happens if APR is 0%?
The payment becomes principal divided by months. You’ll still see how extra principal shortens the term.
Are taxes, insurance, PMI, or HOA fees included?
No. Figures are principal and interest only. You can mentally add escrow items to estimate total out-of-pocket.
What does “Months Already Paid” do?
It advances the baseline amortization first to compute your current balance before applying extra payments going forward.
Can the balance go negative on the last payment?
No. The calculator caps principal and extra so the balance never drops below zero; your final payment may be smaller.
Why is the final payment smaller than usual?
Rounding and the extra principal accelerate payoff; the last installment is adjusted to exactly clear the remaining balance.
How accurate are the payoff dates?
Dates are estimates based on the provided loan start month and monthly cadence. Actual servicer schedules may vary by a few days.
Does extra principal always reduce interest?
Yes. Paying principal sooner reduces the balance that interest is computed on, lowering total interest paid over the life of the loan.
What if I make biweekly payments?
This tool uses monthly periods. A common approximation is to add an extra 1/12th of your payment each month to mimic biweekly acceleration.
Can I model a one-time lump-sum principal payment?
Not directly. As a workaround, apply a large “Extra Principal” for a single month, run the calc, then return it to your usual amount for ongoing months.
Can I compare refinancing scenarios?
This page focuses on extra principal on the current loan. For refi comparisons, you can rerun with a new rate/term and compare KPIs.
Is my data stored or tracked?
No. Everything runs locally in your browser. There are no network requests or analytics.
Why does the Interest Saved percentage change so much with small extras?
Small extra principal early in the loan reduces compounding over many months, so the percent reduction versus baseline can be significant.
What compounding frequency is assumed?
Monthly compounding with payments monthly, which aligns with standard U.S. mortgage servicing.
Do results match my lender exactly?
Servicers may use slightly different day-counts and cutoff times. Treat results as a close estimate, not an exact statement.
Does this work for auto or student loans?
It can model any fixed-rate, fully amortizing loan structure. Just enter the principal, APR, and term.
How do I export and share my schedule?
Use the “Export CSV” button to download the accelerated schedule, then open it in a spreadsheet to save or share.
Is this financial advice?
No. This is an educational tool. Consult a qualified professional for advice tailored to your situation.
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