In the concept of the time value of money, a period is an amount of time between either compounding periods or payments.
Each period represents a payment of an annuity (or perpetuity) and a time when the financial stream compounds.
This calculator does not use a specific formula to calculate the number of payments. It calculates them by using a test number to calculate a present value, then testing the result against the entered present value. Depending on the result, it tests another test number until it comes to a present value that is the same as the entered present value.
The upper bounds of the test number are 11,000 periods and the lower bounds are 0.001 periods.