Sinking Funds: How to Stop "Surprise" Expenses From Wrecking Your Budget
Some months, the budget works perfectly. Then December arrives. Or the car registration renewal. Or back-to-school shopping. Or the annual premium you forgot about.
These aren't really surprises. They happen every year. They just don't happen every month, so they're easy to leave out of the plan. When they show up, they land on a credit card, and the progress you made gets undone.
The fix is called a sinking fund.
What is a sinking fund?
A sinking fund is money you set aside a little at a time for a specific, expected expense. Instead of finding $600 in December for holidays, you save $50 a month all year.
It's different from an emergency fund:
- Emergency fund: unexpected, urgent and necessary (job loss, urgent car repair, medical bill)
- Sinking fund: expected, just not monthly (holidays, registration, annual subscriptions)
Keeping them separate protects your emergency fund for real emergencies.
Step 1: List your irregular expenses
Go through the last 12 months of bank and card statements and write down anything that doesn't happen every month. Common ones:
- Holidays and birthdays
- Car registration and inspection
- Car maintenance: tires, oil changes, brakes
- Insurance premiums paid annually or every six months
- Back-to-school supplies and clothes
- Annual subscriptions and memberships
- Medical and dental costs, like copays and glasses
- Home or rental maintenance
- Pet costs: vet visits, vaccinations
- Travel
- Gifts for weddings, showers and graduations
Step 2: Put a number and a date on each
For each expense, estimate the amount and when it's due. Then calculate:
Monthly amount = Amount needed ÷ Months until due
| Expense | Amount | Due in | Save per month |
|---|---|---|---|
| Holiday gifts | $600 | 12 months | $50 |
| Car registration | $180 | 12 months | $15 |
| Car maintenance | $480 | 12 months | $40 |
| Back-to-school | $300 | 10 months | $30 |
If something is due sooner, you'll need to save more per month this year. Next year will be easier, since you'll start a full 12 months ahead.
Step 3: Add them to your budget
Sinking funds go in the Future You part of your budget, right alongside your emergency fund and retirement. In the example above, that's $135 a month.
If that feels like too much right now, start with the two or three expenses that hurt the most when they show up. Usually that's holidays and car costs.
Step 4: Decide where to keep the money
There are two common setups:
One savings account, tracked separately. Keep all your sinking funds in one savings account and track each category in a spreadsheet. Simple and low-maintenance.
Separate accounts or "buckets." Many banks and credit unions let you create multiple named savings accounts or sub-accounts at no cost. Seeing "Holidays: $350" is motivating and makes it obvious what's available.
Either works. Pick the one you'll actually maintain.
Step 5: Automate it
Set an automatic transfer the day after payday. Once it's running, sinking funds take almost no effort. When the expense arrives, the money is already sitting there.
What it feels like
The first year takes some setup. But the first time your car registration notice arrives and you just... pay it, from money that was waiting for it, without moving anything around or touching a card, you'll understand why people love sinking funds.
It's one of the simplest ways to make a budget feel calm instead of fragile.
Try it
The Goals tab in the Squared Roots Money Toolkit calculates exactly how much you need to save each month for every goal based on its target date, and totals it up so you can compare it with your budget. Get the toolkit.