Inputs
Example data
| Loan | Rate | Term | Extra | Frequency | Interest saved (example) | Payments saved (example) |
|---|---|---|---|---|---|---|
| $250,000 | 6.25% | 30 years | $150 / period | Monthly | $48,000+ | 40+ |
| $120,000 | 5.10% | 15 years | $75 / period | Biweekly | $10,000+ | 20+ |
Formula used
- Periodic rate: r = (annual_rate ÷ 100) ÷ payments_per_year
- Number of payments: n = years × payments_per_year
- Regular payment: Payment = P × r ÷ (1 − (1 + r)−n)
- Per period: Interest = balance × r, Principal = payment − interest
- With extra: Principal_paid = Principal + extra (+ optional lump sum)
How to use this calculator
- Enter your loan amount, annual rate, term, and a start date.
- Choose a frequency (monthly, biweekly, or weekly).
- Add an extra payment amount, then set when it starts and ends.
- Optionally add a lump sum and choose which payment receives it.
- Click Calculate to see savings, payoff date, and the schedule.
- Use Download CSV or Download PDF to save your results.
Payment Mechanics With Extra Amounts
With a fixed-rate loan, each scheduled payment is split between interest and principal. Adding an extra amount increases the principal portion immediately, reducing next period’s interest. For example, on a $250,000 balance at 6.00% with monthly payments, the first month’s interest is about $1,250. If you add $150 extra, the balance drops faster and that interest calculation shrinks sooner.
Interest Savings You Can Measure
Because interest is computed on the outstanding balance, small recurring extras compound. Using the same $250,000, 30-year example, paying $150 extra monthly can save tens of thousands in interest and shorten the term by years, depending on rate and start date. The calculator reports total interest paid, interest saved versus a baseline schedule, and the new payoff date so the benefit is visible, not guessed. Even $50 extra each month can make measurable difference.
Timing Choices That Matter
Frequency affects cash flow and acceleration. Biweekly payments create 26 half-payments per year, which is equivalent to 13 monthly payments, often trimming the payoff even without extra principal. Weekly payments can amplify this effect. If your lender posts payments as received, earlier principal reductions can reduce interest more quickly; if they hold funds until a full payment, the schedule impact may be smaller.
Comparing Baseline And Accelerated Schedules
Baseline amortization assumes no extra principal and runs for the original term. The accelerated schedule layers your extra payment window and any lump-sum event onto that baseline. You can model “extra for 12 months” or “extra until balance under $100,000,” then compare the total paid and remaining balance by date. This side-by-side structure helps prioritize which loan benefits most from extra cash.
Using Exports For Review And Planning
Exports turn the schedule into something you can review and share. The CSV is useful for sorting, pivoting, and checking totals, while the PDF is convenient for printing or emailing. Use the plot to spot where balance declines faster after your extra payments begin, and confirm that a lump sum lands on the intended payment number before committing funds.
FAQs
How is the scheduled payment calculated?
The scheduled payment uses the standard amortization formula based on loan amount, interest rate per period, and number of payments. Extra payments are applied as additional principal after the scheduled payment is allocated.
Does an extra payment change my interest rate?
No. Extra payments reduce principal faster, so less interest accrues over time, but the note rate stays the same. Your lender may have rules for how extra amounts are applied, so confirm principal-only posting.
What is the difference between extra and lump sum?
Extra is a recurring amount applied each payment within your chosen start and end window. Lump sum is a one-time principal payment applied to a specific payment number, useful for bonuses or refunds.
Why do biweekly payments often shorten the term?
Biweekly means 26 half-payments per year, which equals 13 monthly payments. That extra “monthly-equivalent” payment reduces principal faster, typically lowering total interest and pulling the payoff date forward.
Why might my lender’s statement differ from this schedule?
Statements can differ due to payment posting timing, escrow, rounding rules, or lender-specific allocation policies. Use the calculator as an estimate, then compare with your lender’s amortization method and actual posting dates.
What does the graph show?
The graph plots remaining balance over time and cumulative interest paid. You can see where extra payments steepen the balance decline and how the cumulative interest curve flattens as principal falls.