When one is looking around to buy real-estate, loans is something unavoidable for the majority of us. Calculating loans (dutch link) is not black magic, as some banks like you to believe. Below is a JavaScript loan calculator to calculate the missing parameter from the rest. Some calculations can’t be done in one-shot, but need to be resolved iteratively. These are marked “(slow)”. On a descent computer however, these will still run in well under a second.

Calculated numbers are rounded; so doing a forward and backward calculation will probably return slightly different results. The iterative calculations use the current value of the field as starting point, so be sure to fill in something. The interest can be specified over a number of periods: this is useful to calculate the monthly installment from an annual interest rate. This field accepts fractions as well.