Calculator Inputs
Use the responsive form below. It displays in three columns on large screens, two on medium screens, and one on mobile.
Example Data Table
This example helps verify the input structure before running your own scenario.
| Field | Example Value | Meaning |
|---|---|---|
| Home Price | $400,000 | Total property cost. |
| Down Payment | $80,000 | Upfront cash paid by borrower. |
| Loan Amount | $320,000 | Borrowed amount after down payment. |
| Initial Rate | 4.75% | Starting annual mortgage rate. |
| Intro Period | 60 months | Months before rate resets begin. |
| Adjustment Frequency | 12 months | Months between projected resets. |
| Rate Change Per Reset | 0.50% | Expected increase or decrease each reset. |
| Periodic Cap | 2.00% | Largest allowed change per reset. |
| Lifetime Cap | 5.00% | Maximum increase above the initial rate. |
| Rate Floor | 3.50% | Lowest projected rate allowed. |
Formula Used
The calculator uses standard amortization math, then re-amortizes the remaining balance whenever the variable rate resets.
Loan Amount = user loan amount or Loan Amount = Home Price - Down Payment Monthly Rate = Annual Rate / 12 / 100 Payment = P × r / (1 - (1 + r)^(-n)) Interest for Month = Opening Balance × Monthly Rate Principal for Month = Scheduled Payment - Interest + Extra Payment Ending Balance = Opening Balance - Principal Paid Escrow Per Month = Property Tax / 12 + Insurance / 12 + HOA New Rate After Reset = clamp(Current Rate + Rate Step, Floor Rate, Initial Rate + Lifetime Cap)If a periodic cap is entered, the projected rate step is limited to that cap at each reset before the floor and lifetime cap are applied.
How to Use This Calculator
- Enter home price and down payment, or enter a loan amount override.
- Add the initial rate, intro months, reset frequency, projected change, floor, and caps.
- Include annual tax, insurance, HOA, extra monthly payment, and closing costs if needed.
- Press the calculate button to show results above the form and below the header.
- Review the cards, chart, and full amortization table, then export CSV or PDF.
FAQs
1. What makes this calculator variable-rate?
It changes the interest rate after the intro period using your projected reset amount, reset interval, periodic cap, floor, and lifetime cap. Each reset re-amortizes the remaining balance over the remaining term.
2. Does it include taxes and insurance?
Yes. Annual property tax and annual insurance are converted into monthly escrow estimates. Monthly HOA is added too, so you can see a fuller monthly housing cost.
3. Can I model falling rates?
Yes. Enter a negative projected rate change per reset. The floor rate prevents the model from dropping below your chosen minimum.
4. What does the periodic cap do?
It limits how much the rate may move at each reset. Even if your projected change is larger, the calculator restricts that single-step move to the periodic cap value.
5. What does the lifetime cap do?
It limits the maximum increase above the starting rate. This helps estimate a worst-case ceiling for future payment spikes in the scenario.
6. Why do payments change after a reset?
When the rate changes, the loan is re-amortized using the remaining balance, new rate, and remaining term. That produces a new scheduled monthly principal-and-interest payment.
7. Does extra payment reduce interest?
Yes. Extra payment goes straight toward principal in this model. That lowers future interest and may shorten the payoff timeline compared with the same rate path without extra payment.
8. Are closing costs included in monthly payment?
No. Closing costs are tracked separately as an upfront amount. They appear in the summary so you can include them in your overall borrowing review.