Sinking funds: the method that turns the $1,200 'surprise' into $100 a month
Car repairs, a new phone, a flight home, the annual insurance bill. None of them are surprises; they are irregular. A sinking fund is a monthly charge to yourself for a bill you know is coming.
The Federal Reserve's May 2026 household survey put the share of adults who could cover a $400 expense from cash at 63%, a figure that has not moved in four years. What the survey calls an unexpected expense is, on inspection, usually a known expense with an unknown date. Tyres wear out. Phones break. Insurance renews. The sinking fund is the accounting answer to that.
The method
- List every expense that arrives less often than monthly. Annual, quarterly, and the ones that arrive "sometimes".
- Put an annual figure on each — last year's bill, or a reasonable estimate for the ones without one.
- Divide each by twelve. That is the monthly contribution.
- Move the total each month into a separate account, and pay those bills from it when they arrive.
| Expense | Annual | Monthly |
|---|---|---|
| Car repairs and tyres | $1,200 | $100 |
| Car insurance (paid annually) | $1,500 | $125 |
| Phone and laptop replacement | $900 | $75 |
| Holiday travel | $1,800 | $150 |
| Gifts | $600 | $50 |
| Medical deductible | $1,200 | $100 |
| Home or renter's insurance | $480 | $40 |
| Total | $7,680 | $640 |
That is the point of the exercise. A household on $3,000 a month with these irregular costs is spending $640 a month on them whether or not it has budgeted for them. Unbudgeted, the money arrives as a $1,200 car bill in March and goes on a card at 24%. Budgeted, it is a fixed line, and the card is never involved.
Sinking fund against emergency fund
They are different accounts for different events. The emergency fund covers the events that cannot be listed — job loss, a medical event, a family emergency. The sinking funds cover the events that can. Keeping them separate stops a predictable car repair from draining the money set aside for an unpredictable month without income. Where to keep the emergency fund applies to both: somewhere that cannot fall, insured, accessible.
Why one account, not seven
Some people run a separate savings account per fund. Most banks allow it and some are built around it. A single account with a spreadsheet works as well: the balance is one number, the spreadsheet says how much of it belongs to each purpose. What matters is the monthly transfer, which is automatic, and the discipline of paying the irregular bills from that account rather than the current one.
A budget is a list of fixed monthly amounts. Irregular expenses do not fit the list, so they are left out, and then they arrive. A sinking fund makes the irregular expense look exactly like rent: same amount, same day, every month. Nothing about the expense has changed. What has changed is that the budget can now see it.
Sources
- Report on the Economic Well-Being of U.S. Households in 2025 — executive summaryBoard of Governors of the Federal Reserve System · checked Sep 24, 2026