Sinking Funds Explained: Never Get Blindsided by a Predictable Bill Again
A sinking fund is money saved monthly for a known future expense. Divide the cost by the months until it is due, save that amount, and the bill arrives already paid.
A sinking fund is money you set aside every month for a specific expense you know is coming, such as car insurance, holiday gifts or an annual subscription. Divide the cost by the months until it is due and save that amount each month, so the bill arrives already paid instead of landing on a credit card.
December is not an emergency. Neither is a car that needs tires.
Sinking fund or emergency fund?
Both hold savings, but they cover different things. The emergency fund is for the unknown: a job loss, a broken arm, a furnace that dies in January. A sinking fund is for the known: expenses whose amount you can estimate and whose date you can roughly predict. Keeping them separate protects the emergency fund, because when holiday gifts and insurance renewals come out of it, the balance never gets a chance to grow.
Many households have neither. In the Federal Reserve's 2025 Survey of Household Economics and Decisionmaking, 37% of adults said they would not cover a $400 surprise expense entirely with cash or its equivalent, and among those who would pay some other way, the most common method was putting it on a credit card and carrying a balance. A predictable bill paid that way costs interest on top of the bill itself.
The math, with real numbers
- Name the expense and estimate its cost (car insurance: $1,200).
- Count the months until it is due (12).
- Divide: $100 a month.
- Automate that transfer on payday, and pay the bill from the fund when it arrives.
Three funds make the idea concrete. Say your car insurance is $1,200 a year and you pay it in one lump in April. Last year you also spent $1,020 on car repairs (a set of tires, brakes, an oil change or two), and holiday gifts came to $600. Divide each by 12: $100, $85 and $50, or $235 a month in total.
If your insurance is due in eight months rather than twelve, the monthly amount for that fund rises to $150 until the first renewal, then drops back to $100 once you are on a yearly cycle. The point is that nothing in the list is a surprise. You already know roughly what each one costs; the fund just spreads it out.
Estimating is easier than it sounds. Look back at the last twelve months of statements and pull out every charge over $200 that was not rent, groceries or a regular bill. Most of what you find will repeat next year.
Which sinking funds should you start with?
Start with the expenses that hurt most last year. Most households end up with some version of these:
- Car: repairs, tires, registration, and insurance if you pay it yearly. The Bureau of Labor Statistics' Consumer Expenditure Survey for 2025 puts average US spending on vehicle costs other than buying the car and fuel, such as insurance, repairs and licensing, at $4,765 a year.
- Holidays and gifts: December, birthdays, weddings.
- Annual bills: subscriptions, memberships, property tax, anything that renews yearly.
- Travel: saved before you book rather than paid off after.
- Clothing: Statistics Canada's Survey of Household Spending found Canadian households spent an average of $2,739 on clothing and accessories in 2023.
- Home and health: the appliance that will eventually fail, dental work, glasses, the vet.
Opening twelve sinking funds at once and spreading $100 across all of them means none of them fills. Pick the three expenses that hurt most last year, fund those, and add more once the habit is boring.
Do sinking funds count as savings?
Yes: in a 50/30/20 budget they come out of the 20% savings bucket, alongside the emergency fund and long-term investing. Order matters when a month runs tight. Build a starter emergency fund first, then fund the nearest and most certain sinking funds, then longer-term goals.
When a fund comes up short
Estimates miss. If the repair is $1,400 and the fund holds $900, pay the gap from the emergency fund or this month's wants, then raise next year's monthly amount.
Leftover money is the happier problem. If the car needed less than you saved, keep the surplus in the fund as a head start on next year, or move it to the emergency fund if that is still below target. Spending it on something unrelated is how a sinking fund turns back into a general savings account that gets raided.
Where to keep the money is a matter of taste. Some people open a separate high-interest savings account for each fund so the balances never mix. Others keep every fund in one savings account and track the split on paper or in an app, which is simpler but only works if you trust the tracking. Either way, keep sinking fund money out of your everyday chequing account, where a $900 balance looks like spending money. And if your income is irregular, build the monthly sinking fund amounts into the budget you run on a lean month, since the bills they cover arrive on schedule whether the month was good or not.
Setting up sinking funds in otterfund
In otterfund, a sinking fund is a goal with a target and a rank. Add car insurance at $1,200 and rank it after the emergency fund, and the savings share of each paycheck reaches it in that order. A progress bar per fund answers 'is December already paid for?' at a glance, and goals are part of the free plan, so the first fund can start this payday.