Use this calculator to identify your ‘Financial Safety Window.’ By modeling projected rate movements, you can estimate the exact month and interest rate level where a lower starting rate would begin to result in a financial loss compared to a fixed rate. This clarity helps you decide between the flexibility of a short-term variable rate or the security of a long-term fixed rate.

Name: (Optional)
Loan:	Borrowing amount.	Term:	Mortgage term for repayment calculation.
Rate1:	Variable or discounted rate to compare.	Rate2:	Alternate fixed rate.
Increase (fixed):	Under normal circumstances Bank of England sets rate changes by 25 basis points at a time.	Every / months:	Your prediction for how often rate changes will happen e.g 3 = every 3 months. This setting can also be used to manage larger rate changes by shortening the period.
Rate Term:	Default set for 2 years.
Saving / m:	Monthly gain / loss while the rate is lower.	Saving / Period:	Total gain / loss per period.
Breakeven Month:	Calculates the “Crossover Point” where the early-term interest savings are fully offset by later-term rate increases.	Breakeven Rate:	Same as breakeven month, but for the rate.
Breakeven Monthly:	The point to which monthly payments needs to rise before resulting in a loss.