Compare locking now with floating
Use the rate you can lock today and a realistic floating scenario from current lender pricing. This is not an APR calculator and does not replace your Loan Estimate.
| Cost item | Amount | Notes |
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Methodology notes
Payment math
Monthly principal and interest use the standard fixed-rate amortization formula from loan amount, rate, and term.
Lock cost
Total lock cost adds flat lock fees, lock points, projected extension fees, extension points, and float-down fees when the lower-rate scenario applies.
Break-even
Break-even divides total lock cost by monthly savings when the locked rate is lower than the floating scenario.
Rate volatility, lender lock agreements, extension policies, float-down rules, lock expiration, discount points, lender credits, and APR treatment can change the real result. The official lender quote, Loan Estimate, Closing Disclosure, and written lock agreement control. PlainFigure may earn a commission from partner links, but calculator formulas are independent. See full disclosure.
Mortgage rate lock FAQ
Should I lock or float?
Locking tends to make sense when the avoided payment risk is larger than lock and extension fees over your expected holding period. Floating can win if rates fall enough and your closing timeline is flexible.
How do extension fees work?
Some lenders charge a daily fee, a fraction of a point, or both when the loan does not close before the lock expires. Ask for the deadline and extension price in writing.
How is this different from points?
Points compare paying upfront for a lower note rate. This calculator focuses on timing risk: locking today's quote versus accepting whatever rate is available later.