How we calculate

Inputs and assumptions

Each calculator lists its units, input limits and assumptions. If a value is missing or out of range, an error explains what to change.

Money and dates

The loan calculator uses decimal arithmetic and rounds monthly amounts to cents. Date calculations count calendar days, so local clock changes do not affect the count.

Examples and checks

Automated tests cover worked examples, input limits and invalid values. Each calculator links to its sources and shows which version of the method was checked.

Using an estimate

The fixed-rate loan tool covers principal and interest. It excludes taxes, insurance, fees and variable interest rates; a lender's actual schedule may differ.