Most household budgets are built around the bills that arrive every month: the mortgage or rent, energy, council tax, broadband, and the loan repayment that leaves your account on the same date without fail. The costs that cause real trouble are the ones that refuse to be monthly — the MOT, the boiler service, the insurance renewal, Christmas, the wedding invitation that lands in March for a ceremony in August.

What a sinking fund actually is

A sinking fund is money you set aside in small, regular amounts for an expense you know is coming but cannot pay monthly. The name comes from accounting and sounds gloomier than it is. In practice it is simply a savings pot with a job attached.

It is worth separating this from your emergency fund. An emergency fund covers the genuinely unexpected — the boiler that fails without warning, the job that ends suddenly. A sinking fund covers the predictable but irregular. You know the money will be needed. You just do not know the exact date or amount.

Common sinking fund targets include:

• Car costs — MOT, annual service, tyres, breakdown cover, insurance excess
• Home costs — boiler service, buildings and contents insurance, replacing a washing machine or fridge
• Family occasions — Christmas, birthdays, school uniforms, family holidays
• Personal costs — dental check-ups, glasses, annual subscriptions, professional fees

Why this matters more when you are repaying a loan

A personal loan works well because the repayment is fixed. You know what leaves your account each month, and budgeting becomes simpler. The difficulty is that a fixed repayment also leaves less room for surprises. If you are paying £220 a month towards a loan and the car fails its MOT with £450 of advisory work, that month can become genuinely tight.

Missed or late loan payments are costly in more ways than one. There is usually a late payment charge, interest continues to accrue, and the missed payment is recorded on your credit file. A pattern of missed payments makes future borrowing more expensive, or closes the door on it entirely.

A sinking fund does not increase your income. It changes the timing. Money set aside in a calm month does the work of a bill in a difficult one, and your loan repayment carries on untouched.

Working out your own irregular costs

The honest way to do this is to look backwards rather than guess. Dig out twelve months of bank statements and highlight everything that was not a monthly direct debit or standing order.

• Note each irregular cost and roughly when it comes round again
• Add anything you expect but have not paid for yet — a new tyre, a replacement laptop, a dental crown
• Include the seasonal costs people routinely underestimate, such as Christmas and summer holidays

For a sense of scale, an MOT is capped at £54.85 for a car, a full service typically runs £150 to £300, a pair of mid-range tyres fitted is £120 to £200, home insurance averages £150 to £250, and a boiler service is usually £80 to £100. Christmas for a family of four can easily reach £500 to £700 once gifts, food and travel are counted.

Turning a yearly bill into a monthly amount

Once you have your list, divide each annual figure by twelve and round up. Rounding up builds a small buffer against price rises.

• Car insurance at £480 a year becomes £40 a month
• MOT and service at £300 becomes £25 a month
• Christmas at £600 becomes £50 a month
• Home insurance at £180 becomes £15 a month

That is £130 a month for four costs that would otherwise arrive as sudden, unwelcome hits. If £130 is impossible right now, do not abandon the idea — pick the single expense that has hurt most in the past and fund that one first.

Where to keep the money

The pot needs to be separate enough that you do not spend it, and close enough that you can reach it when the bill lands. A second instant-access savings account with your existing bank is usually the simplest solution, and many providers let you label pots with a name.

Keep it accessible. This is not investing, and the goal is certainty rather than growth. A little interest is a bonus, not the point. Avoid locking the money into a fixed-term account that matures after the MOT is due.

Name each pot after its job — "car", "Christmas", "house" — so that dipping into it feels like breaking a promise rather than moving numbers around.

Starting small and adjusting as you go

If money is already stretched, begin with £10 or £20 a month. The habit matters more than the amount in the early months. A tenner a month is £120 a year, which covers an MOT and a service on a small car.

Review your sinking funds every three to six months. Premiums change, children grow, cars age. If a bonus, tax rebate or overtime payment lands, top up the pots that are furthest behind.

And when you make the final repayment on a personal loan, consider redirecting that monthly amount straight into your sinking funds. It is money you have already proved you can live without, and it turns the end of a loan into the beginning of real breathing space.