Timing of payments
An annuity due differs from end-of-period payments because of when the payments occur. If the number of payments, rate and final date are the same, each beginning-of-period payment participates in one additional accrual compared with an end-of-period payment.
Model comparison
In a constant-rate educational model, the ordinary-annuity result is multiplied by one period-growth factor. This is not an additional contribution. A common mistake is to add a payment at the initial moment while keeping all earlier payments, thereby increasing the number of payments and comparing different amounts of the person’s own money.
Contract timing
The Investor.gov calculator separately identifies the monthly contribution and the compounding frequency.[1](#source-savx-compound) Its fields do not by themselves establish a bank’s treatment of a particular transfer. A real contract requires the date on which the interest base changes. The term describes the timing structure of a mathematical model, not an obligation or recommendation to pay earlier than necessary household expenses.