The Bills That Break Budgets
Most budgets handle monthly bills fine — rent, utilities, subscriptions. What derails them are the irregular ones: the annual car insurance premium, the boiler service, Christmas, the car MOT, a holiday deposit. These expenses are entirely predictable, yet because they do not arrive monthly, they feel like surprises — and surprises get put on credit cards. A sinking fund is the simple fix: a pot of money you build gradually so the cash is waiting when the bill lands.
What Is a Sinking Fund?
A sinking fund is money you set aside regularly for a specific, known future expense. Unlike an emergency fund — which covers genuinely unexpected events like a job loss (see our guide on sizing your emergency fund) — a sinking fund is for costs you can see coming. You know roughly what they will cost and roughly when they are due; you just spread the saving across the months in between.
Common candidates include:
- Annual or semi-annual insurance premiums
- Car tax, servicing and repairs
- Home maintenance (boiler service, appliance replacement)
- Christmas, birthdays and other celebrations
- Holidays
- School expenses — uniforms, trips, supplies
- Medical or dental costs you pay out of pocket
- Pet expenses such as annual vet bills
How to Set Up Sinking Funds in 5 Steps
1. List your irregular expenses for the next 12 months
Go through last year’s bank statements and note every non-monthly bill: the amounts and the months they fell due. Add the celebrations and events you know are coming this year.
2. Estimate the cost of each
Use last year’s figure as a starting point and add a small buffer — around 10% — in case prices have risen. A rough-but-generous estimate beats a precise-but-short one.
3. Divide by the months remaining
This is the core calculation. If your car insurance renewal is $900 in eight months, you need to set aside $112.50 per month. Do this for each fund and add up the monthly totals — that is your sinking-fund line in the budget.
4. Keep the money separate
Money that sits in your main current account tends to get spent. Keep sinking funds in a separate savings account — ideally one that lets you create named pots or sub-accounts, one per goal. If you are starting from scratch, our walkthrough on building your first monthly budget shows where this line item fits.
5. Automate the transfers
Set up an automatic transfer for the day after payday. Automation removes willpower from the equation: the money moves before you have a chance to spend it.
Sinking Funds vs Emergency Fund: Do You Need Both?
Yes — they do different jobs. The emergency fund is your safety net for true surprises; the sinking fund is your plan for predictable-but-lumpy costs. In fact, sinking funds protect your emergency fund: without them, every “predictable surprise” raids the emergency pot, and it never reaches its target. Think of sinking funds as the first line of defence and the emergency fund as the last.
How Many Sinking Funds Should You Have?
Start with three to five of your biggest irregular expenses — the ones that have hurt most in the past. You can run them as separate pots for clarity or as one combined “irregular bills” pot if you prefer simplicity. As the habit beds in, add more. Some people eventually run a dozen small funds; others keep it to a handful. Either approach works as long as the maths is honest.
Tips to Make Them Stick
- Start small. Even $25 a month toward Christmas beats a January credit card bill.
- Revisit the amounts yearly. Premiums rise, cars age, kids grow — update your estimates.
- Do not borrow from a fund for unrelated spending. If you raid the car-repair pot for a weekend away, the bill still arrives.
- Celebrate the wins. Paying a big bill from savings, with zero stress, is the reward — notice it.
- Trim the totals first. Before funding everything at last year’s prices, look for savings — our tips on cutting everyday spending without feeling deprived apply to irregular bills too.
For a second opinion on the method, the UK’s official MoneyHelper service has a clear step-by-step guide: Sinking funds explained — MoneyHelper.
The Bottom Line
Sinking funds turn budget-busting surprises into boring, manageable monthly transfers. List your irregular expenses, divide each by the months until it is due, automate the saving, and keep the money separate. Within a year, the bills that used to cause panic will barely register.
This article is for general information only and is not financial advice. Consider speaking to a qualified adviser about your own circumstances.