Calculator Inputs
Example Data Table
| Loan | Rate | Term | Frequency | Extra/period | Interest saved | Time saved |
|---|---|---|---|---|---|---|
| $250,000 | 6.50% | 30 years | Monthly | $150 | $60,000+ | 6+ years |
| $180,000 | 5.25% | 20 years | Biweekly | $50 | $15,000+ | 2+ years |
| $90,000 | 7.10% | 15 years | Weekly | $25 | $8,000+ | 1+ year |
Formula Used
n = term_years × periods_per_year
PMT = P × r / (1 − (1+r)−n)
Total Payment = PMT + Extra
Principal = Total Payment − Interest
New Balance = Balance − Principal
How to Use This Calculator
- Enter your loan amount, interest rate, and term.
- Choose a payment frequency that matches your lender schedule.
- Add extra payments, lump sums, or a one-time extra if desired.
- Optionally round payments up to create automatic extra principal.
- Click Calculate savings to view results above.
- Download CSV or PDF exports for sharing and recordkeeping.
Payment baseline and rate sensitivity
At 6.50% APR on a $250,000 balance, the first monthly interest charge is about $1,354, so early payments mostly cover interest. A 1.00% rate increase raises the required payment and can add tens of thousands in lifetime interest. Small changes compound over decades. The graph highlights when principal overtakes interest, usually after the early years. Use the rate field to test refinancing scenarios and to see how quickly interest drops as the balance falls.
Extra principal and interest savings
Every extra dollar reduces principal immediately, so future interest is computed on a smaller balance. For a 30‑year loan, adding $150 per month often saves more than $50,000 in interest and shortens payoff by several years. The calculator separates required payment from “extra” so you can see whether savings come from rounding, recurring extras, or lump sums.
Frequency effects and acceleration
Switching to biweekly or weekly changes both the per‑payment rate and how often principal is applied. A biweekly plan produces 26 payments per year, which typically behaves like making one extra monthly payment annually. The payoff date and total periods update automatically, letting you compare time saved under each frequency.
Rounding strategy and budget control
Rounding up to the nearest $10, $25, or $50 creates “invisible” extra payments without new habits. If the computed payment is $1,579.42 and you round to $1,600, the $20.58 difference goes directly to principal. Use round increments that fit payroll cycles and avoid overdrafts. Pair rounding with an “extra starts after” delay to match seasonal income or a planned raise.
Lump sums and payoff timing
Annual or one‑time lump sums act like step changes in principal. A $2,000 annual lump typically has a bigger impact when applied early because it reduces interest for more remaining periods. A one‑time $5,000 bonus can also eliminate multiple future payments near the end. Use the charts to confirm the balance curve bends downward after each lump, and export schedules to document your payoff plan.
FAQs
Does paying biweekly always save interest?
Often yes, because 26 payments per year reduce principal sooner. Savings depend on whether your lender applies payments immediately and whether fees apply. Use the frequency option to compare total interest and the payoff date side by side.
What does “round payment up” change?
Rounding increases your actual payment to the next increment you choose. The difference is treated as extra principal each period, lowering the balance faster and reducing interest over time without changing the loan rate.
How are annual lump sums applied?
The calculator applies the lump sum every 12, 26, or 52 payments based on your frequency. It is added to that period’s payment and goes to principal after interest, accelerating payoff.
Why is my schedule showing negative amortization?
If the planned payment plus extras is smaller than the interest due, the balance can grow. Increase the payment, reduce the extra delay, or verify the rate and term. Some loans also have minimum payment rules.
Do CSV and PDF exports include the full schedule?
CSV exports include the entire schedule you see. PDF exports include the summary and the first 150 rows to keep files compact. Use CSV for full archival records and PDF for sharing snapshots.
Is this an official lender payoff quote?
No. Results are estimates using standard amortization math and your inputs. Actual lender statements can differ due to escrow, day-count conventions, rounding rules, and timing of extra payments.