Calculator
Sinking fund calculator
A sinking fund is money you set aside a little at a time for a cost you know is coming, such as an annual insurance bill, car maintenance, gifts or a trip. Enter each cost, how many months you have until it is due, and anything you have already put aside. The page works out the monthly amount for each fund and the total. It uses only your numbers and sends nothing anywhere.
Type at least one yearly or occasional expense amount to see what to set aside each month. With scripts turned off, do it by hand: subtract what you have saved from the amount needed, then divide by the months left.
Before you decide
The result is only as good as your estimates. Use the real bill where you have it, and a cautious guess where you do not, then correct the number when the bill arrives. Keep sinking funds separate from your emergency savings so one does not quietly spend the other.
How the calculator works
For each row the page does three steps. First it subtracts the amount already saved from the amount needed, and treats a negative answer as zero, so a fund that is already fully covered asks for nothing more. Second it divides what is left by the months until the cost is due. If you leave the months at 12, that is the familiar rule of dividing a yearly cost by twelve. Third it rounds the monthly figure up to the next cent, so that saving that amount every month never leaves you slightly short. The total is the sum of the monthly figures.
Rows with no amount are skipped. A months figure that is blank, below 1 or not a number is treated as 12, and decimals are rounded down to a whole number of months.
Choosing what becomes a fund
Good candidates are costs that are certain but not monthly: annual or semi-annual insurance, vehicle registration or maintenance, subscriptions billed yearly, medical or dental costs you expect, gifts and holidays, and home repairs. A cost you cannot predict at all belongs in a general emergency buffer instead. Eight rows is deliberate. Many small funds are hard to keep up, so group related costs into a few broader funds, for example one fund for the car and one for the home. The article on using sinking funds without overcomplicating your budget explains how to group them, and budgeting for irregular expenses covers finding the costs in the first place.
Fitting the total into your budget
Compare the monthly total with your plan. If it is more than you can afford, you have three honest options: extend the months for costs that are not due soon, trim the estimate for costs that are flexible, or fund the most urgent costs first and add the others later. If your income varies, use the irregular income baseline calculator to decide what your plan can safely rely on before you commit to monthly amounts.
Limits
- It does not add interest. If you keep funds in an account that pays interest, your real cost will be slightly lower, but treat that as a bonus rather than part of the plan.
- It does not adjust for price changes. Costs often rise, so review your amounts once or twice a year.
- It cannot tell you which costs matter most to your household or how to prioritize against debts. See emergency fund versus debt for that question.
- It is general information, not financial advice.
Where this comes from
The method (divide the cost by the months remaining after subtracting what is saved) is plain arithmetic, and the idea of setting aside money each month for annual bills appears throughout consumer budgeting education. We read several credit union and financial education pages that describe it, but no single named standard defines the formula. The round-up to the next cent and the zero floor for fully funded rows are our own choices to avoid small shortfalls and negative amounts.