What a sinking fund actually is
A sinking fund is money you set aside on a schedule, on purpose, for an expense you know is coming — as opposed to your emergency fund, which covers what you don't see coming. A new roof in five years, a car that'll need replacing, the property tax bill that lands every December, an annual insurance premium — these aren't emergencies, they're certainties with a date attached. The calculator above answers the only question that matters for each one: how much do I need to set aside every month between now and then?
Why lumping them into "savings" backfires
Most people who don't use sinking funds fall into one of two traps: they get blindsided every December when property tax is due, pulling from a credit card or wherever cash happens to be sitting, or they keep one undifferentiated savings balance and can't tell how much of it is actually earmarked versus free to spend. Naming each fund and tracking it separately — even just as line items in one account — fixes both problems. When the roof fund hits its target, you know it's really there, because nothing else has been quietly borrowing from it.
The math behind the required monthly number
For each fund, the calculator solves for the level monthly contribution that grows your current balance plus ongoing payments to exactly your target by the deadline. With no interest (APY of 0, which is fine for anything under a year or two), it's simply (target − already saved) ÷ months remaining. With an APY entered, the calculator accounts for interest compounding monthly on the growing balance, so the required contribution is slightly lower than the simple division — the earlier dollars have more time to earn.
Where to actually keep the money
Sinking funds work best in a high-yield savings account, separate from your everyday checking — separate enough that you have to deliberately transfer money out to spend it, but liquid enough to access without penalty when the date arrives. Many banks let you open multiple named "buckets" or sub-savings-accounts for exactly this purpose; if yours doesn't, a shared spreadsheet tracking each fund's target and balance does the same job. Once you've named your funds and know the totals, our 50/30/20 budget calculator can show you where the combined monthly total fits against your income.
Frequently asked questions
- How is a sinking fund different from an emergency fund?
- An emergency fund covers the unexpected — job loss, medical bills, a surprise repair — and should stay liquid and untouched otherwise. A sinking fund covers the expected: a specific expense with a roughly known amount and date, like a car replacement or annual insurance premium. You should have both, and they should be tracked separately.
- Should I use one sinking fund account or several?
- Either works as long as you know how much of the balance belongs to each purpose. One account with a spreadsheet tracking each fund's target and progress (like the table above) is simplest; several named sub-accounts at a bank that supports them makes the separation automatic and harder to accidentally raid.
- What if my expense estimate turns out to be wrong?
- Revisit it periodically — property tax bills and insurance premiums usually creep up a little each year, and a car replacement estimate might shift with the market. Update the target amount above and recalculate; better to catch a shortfall with 18 months of runway left than with one.
- Should I include interest (APY) in the calculation?
- Yes if the fund sits in a high-yield savings account and the timeline is a year or more — it modestly lowers the required monthly contribution. For short timelines (property tax due in a few months) it barely matters, so 0% is a fine simplification.