To replenish refers to refilling a depleted cash box in a petty cash system. A petty cash box or drawer is usually assigned a fixed amount of petty cash, which is the maximum amount of cash that should ever be found in it. When petty cash is distributed in exchange for receipts or vouchers, the amount of cash in a location declines. Eventually, the petty cash location is replenished when the receipts and vouchers are replaced by cash, thereby "topping up" the petty cash box to its original designated level. The replenishment amount may change if the assigned amount of cash for a petty cash box is altered (usually resulting from an examination of petty cash usage).

Thus, the replenishment process shifts cash from a central cashier location to one or more petty cash locations, where it is drawn down as incidental expenses are paid.

For example, a petty cash box has a target balance of $300. The petty cash custodian pays for a number of expenses, reducing the cash balance by $275. A replenishment transaction places an additional $275 of cash into the petty cash box, bringing the petty cash balance back to its target level of $300.