budgeting basics
Sinking Funds Explained: Save for the Known Unknowns
Every budget has a blind spot, and it is always the same one: the expenses that are not monthly. Car insurance, Christmas, the friend's wedding in another country, the annual software renewal, the dentist. They arrive with complete predictability, and every year they behave like a surprise. Sinking funds are the fix — small monthly savings pots, one per known future expense, that turn "oh no, it's March" into "already paid for".
What a sinking fund is (and is not)
A sinking fund is money you set aside each month for a specific, expected, non-monthly cost. The name comes from accounting — companies "sink" money gradually to retire future obligations — but the household version is simpler: if the car service costs £360 every March, you save £30 a month, every month, and March stops being an event.
It is not an emergency fund. The emergency fund is for the things you cannot predict; sinking funds are for the things you absolutely can. Mixing them is the classic mistake — you drain the emergency pot for a planned holiday, and then a genuine emergency finds the pot empty.
Which funds to start with
Start with the expenses that have ambushed you before. For most young professionals the first four cover 90% of the damage:
- Car or transport: insurance, MOT, services, tyres — or for non-drivers, the annual railcard, bike maintenance, occasional taxis.
- Gifts and Christmas: add up last December honestly, including birthdays through the year, and divide by twelve.
- Travel and occasions: weddings, hen dos, the family trip. These are the costs people most often put on a card.
- Annual bills: any subscription or insurance paid yearly, divided by twelve so the renewal month is invisible.
Later you can add home deposits, a replacement-tech fund, vet bills, or a "flat deposit for the next move" pot. The system scales; the first version should fit on one line each.
How to run them without a spreadsheet degree
- List the costs and their months. Go through last year's bank statements and note every non-monthly hit over £50.
- Divide each by twelve (or by the months remaining until it lands, if that is fewer).
- Total them and automate. One standing order on payday into a separate easy-access savings account, or into pots if your bank offers them. Labelled pots are ideal — the whole point is that the Christmas money is visibly not the car money.
- Spend from the pot, not the card. When the expense lands, transfer it out. The month's budget never notices.
Inside a 50/30/20 budget, sinking funds live in the 20% savings share alongside your emergency fund. If £150 a month is too much on day one, fund the two most painful categories first and add the rest after your next pay rise.
Sizing each fund honestly
The maths per fund is simple — annual cost divided by twelve — but the estimate it starts from is where people go wrong. Use last year's actual figure, not the optimistic one: open last December's statement for the Christmas fund, last year's renewal letter for the insurance. If the cost is new (a first car, a first pet), price it properly rather than guessing; a sinking fund built on a fantasy number is just a smaller ambush.
Review the sizes once a year. Premiums rise, gift lists grow, and a fund that was right last March can be 20% short this March. Topping up a pot by a few pounds a month at review time is painless; discovering the shortfall at the till is not.
A note on joint costs: if you share expenses with a partner or flatmates, sinking funds work best when each person runs their own for shared annual costs, or when one shared pot gets two standing orders. The failure mode is assuming the other person is saving it — say the number out loud once and automate it twice.
Resist the urge to open ten funds at once. Each pot is a small mental commitment, and a long list of underfed funds feels worse than a short list of healthy ones. Three or four well-chosen pots beat a dozen anaemic ones.
What they are not good for
Sinking funds are for costs with a date or a near-certain arrival. They are a poor fit for vague aspirations — "holiday someday", "maybe a new bike" — because a pot without a target quietly becomes spare cash, and spare cash gets spent. Give the aspiration a number and a rough date first, and it earns its fund.
Why this feels like a pay rise
The first full year with sinking funds is oddly anticlimactic: the car insurance renews and nothing happens. Christmas arrives and nothing happens. The annual phone bill lands and, again, nothing happens. That flatness is the entire product. People consistently report that sinking funds reduce money stress more than the same amount added to general savings, because the stress was never about the total — it was about the ambush. Pair the pots with a monthly money date to top up any fund that ran short, and the "surprise" expense becomes a solved problem — permanently, and for the price of one standing order.