Sinking funds turn big, irregular expenses into bite-sized, predictable savings goals. Instead of being surprised by a $3,600 car repair or an annual insurance bill, you set aside the same small amount each month until the total is reached. Practically, this increases the chance you’ll have cash when you need it and avoids costly emergency credit. Behavioral economics calls this “mental accounting”: labeling money for a purpose increases discipline. To figure out how long a goal takes, divide the target by your monthly contribution; for targets that are multiples of round contributions, the calendar math is straightforward. This question is a practical test: given a set contribution and a target, how many months until the goal is met? It’s the kind of calculation people do when deciding whether to cut discretionary spending or delay other goals.