Rough; confirm with your contract.
Annual miles are prorated by elapsed lease months: allowed so far ≈ (annual/12)×months_elapsed. Compare to odometer_now − odometer_start. Inputs must be consistent: positive annual miles, positive term length, 0 ≤ elapsed ≤ term, numeric odometers.
This calculator uses plain decimal numbers. If a result looks wrong, check whether you used a comma instead of a dot (or vice versa) where the field expects one.