ToolGrym field guide
ARM vs. Fixed-Rate Mortgage
An ARM may start below a fixed-rate mortgage, but the relevant comparison includes the future payment, caps, and the time you expect to keep the loan.
- Format
- Plain-English explainer
- Practice
- 3 linked calculators
Written by the ToolGrym Editorial Team
Last reviewed:
Compare two payment paths
Use the ARM calculator to show the initial payment and a reset scenario. Compare it with the fixed mortgage calculator on the same balance and term.
Read the caps
The note should disclose the initial, periodic, and lifetime caps, plus the index, margin, and adjustment period. A lower first payment is not protection from a later increase.
Match the loan to the horizon
An ARM can be reasonable for a borrower who understands the risk and expects to move or refinance, but a move or refinance is never guaranteed. Stress-test income and rates before deciding.
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The ToolGrym editorial team builds and maintains every calculator on this site. Each tool’s formulas are implemented as tested code and verified against authoritative sources such as the CFPB, Federal Reserve, IRS, and BLS.