How to use this calculator
Key takeaways
04 · ideas- Extra Payments tab shows exact interest savings
- Scenarios tab compares up to 4 loan configurations side by side
- Export tab generates a full PDF report with charts
- Refinance tab calculates your break-even point
Basic level
The essentials · 1 min
This calculator has 6 tabs: Basic, Extra Payments, Rates, Expenses, Scenarios, and Export.
- Basic — Enter loan amount, term, and rate to get your monthly payment instantly.
- Extra Payments — Simulate paying more each month and see how much interest you save.
- Rates — Model variable-rate loans with multiple rate tranches.
- Expenses — Add property tax, insurance, and HOA to see your true monthly cost.
- Scenarios — Compare up to 4 different loan configurations side by side.
- Export — Download a full PDF report with charts and tables.
Start with the Basic tab. Enter your loan amount, interest rate, and term. The summary panel on the right updates instantly with your monthly payment, total interest, and a breakdown chart.
Intermediate level
How it applies · 2 min
Extra Payments tab
This is where the real savings happen. Enter a monthly extra payment amount — even $100/month — and the calculator instantly shows:
- How many months you'll cut off the loan
- Total interest saved over the life of the loan
- A balance comparison chart (with vs. without extra payments)
You can also add lump-sum payments (one-time extra payments) for any month. This is ideal for modeling annual bonuses, tax refunds, or inheritance.
Try it: on a $200,000 loan at 7.5%, paying an extra $300/month saves $86,000 in interest and cuts 8 years off the loan.
Rates tab
Use this when you have an adjustable-rate mortgage (ARM) or expect to refinance partway through. You can add multiple rate tranches — for example:
| From month | Rate |
|---|---|
| 1 | 5.5% |
| 61 | 7.0% |
| 120 | 6.25% |
The calculator applies each rate to the correct period and shows you the full payment trajectory.
Scenarios tab
Compare up to 4 loan options simultaneously. Useful for:- 15-year vs 30-year mortgage
- Different down payment amounts
- Fixed vs ARM strategy
- Different lenders' offers
Each scenario shows its monthly payment, total interest, and payoff date in a single comparison table.
Advanced level
The math, step by step · 1 min
Expenses tab and true cost of ownership
The basic P&I payment is only part of your monthly housing cost. The Expenses tab adds:
- Property tax — typically 0.5–2.5% of home value annually
- Homeowner's insurance — typically $1,000–$2,500/year
- HOA fees — $0–$1,000+/month depending on community
- PMI — if down payment < 20%, adds 0.5–1.5% of loan annually until LTV reaches 78%
This gives you your true PITI (Principal + Interest + Taxes + Insurance) — the number lenders use to calculate your housing ratio (target: < 28% of gross income).
Export and PDF report
The Export tab generates:- A PDF report with all charts, amortization schedule, and scenario comparison
The PDF includes an executive summary with your total cost, breakdowns by scenario, and the amortization schedule. Useful for presenting to a financial advisor or keeping in your mortgage records.
Saving simulations
Use the 💾 Save button in the header to save your current simulation. You can store multiple configurations (different rate scenarios, payment strategies) and reload them later. Saved simulations persist in your browser's local storage.