APR Calculator for Adjustable Rate Mortgages
For an ARM, the APR reflects the initial rate plus your upfront fees. Use it to compare ARM offers on a consistent basis.
A worked example
Running this tool on current national benchmarks (Federal Reserve / Freddie Mac via FRED (St. Louis Fed)) — swap in your own numbers to see how the result moves.
- Loan amount
- $320,000
- Initial rate
- 5.50%
- Loan term (years)
- 30
- Discount points
- 1
- Other closing fees
- $2,800
versus a 5.50% initial rate
- Initial rate5.50%
- APR (initial)5.672%
- Points cost$3,200
How the initial-rate APR changes with loan amount
Holding the other inputs at the example above, here is how the result moves as loan amount changes.
| Loan amount | Initial-rate APR | Initial rate |
|---|---|---|
| $150,000 | 5.765% | 5.50% |
| $250,000 | 5.695% | 5.50% |
| $325,000 | 5.671% | 5.50% |
| $475,000 | 5.646% | 5.50% |
| $650,000 | 5.631% | 5.50% |
The math behind it
The calculator adds your discount points (points times 1% of the loan) to your other closing fees to get the total upfront cost. It then solves for the annual rate that makes the loan's cash flows balance once those fees are treated as part of the cost of borrowing — the APR — using the initial rate and the full term. The result is the APR against your quoted initial rate.
Assumptions & limits
- The APR is based on the ARM's initial rate only. It does not account for the rate adjusting upward later, so it understates the loan's true long-run cost.
- One discount point equals 1% of the loan amount; that cost is added to your other fees before solving for the APR.
- Every upfront fee you enter is treated as a finance charge spread across the full term at the initial rate.
- The monthly payment shown is based on the initial note rate, not the APR. Taxes, insurance, and mortgage insurance are excluded.
Source: Freddie Mac PMMS via FRED. Annual averages; latest weekly reading shown.
Common questions
Why is the ARM's APR less useful than a fixed loan's APR?
APR assumes the rate stays put for the whole term, which is true for a fixed loan but not an ARM. Because it uses only the low intro rate, an ARM's APR ignores the higher payments that arrive after the reset. Treat it as a starting comparison, then also compare the margin, caps, and fully-indexed rate.
Does a lower APR always mean the cheaper ARM?
Not necessarily. Two ARMs can show similar APRs but carry very different margins and caps, which decide what you actually pay after the fixed period. The APR captures the upfront fees well but says nothing about reset risk, so compare those terms separately.
Should I pay points on an ARM I plan to sell early?
Usually no. Points lower your rate but take years to recoup through savings. If you expect to sell or refinance before the fixed period ends, you may never break even on the points, so a higher-rate, lower-fee option can cost less overall.