Sinking Funds 101: How to Stop September From Ambushing You Every Year
It happens every August. You're cruising along, summer's winding down, and then - uniform, shoes, a new bag because the old one's held together with hope, a ‘voluntary contribution’ for a school trip that feels remarkably non-voluntary, stationery lists, PE kit, maybe a laptop or a calculator for the older ones. It lands all at once, feels like a financial mugging, and you tell yourself next year I'll be ready for this.
And then next year, you're not, because you never actually built that system.
This is exactly what a sinking fund is for.
It’s not glamorous or exciting, but it’s genuinely one of the most useful tools in your money kit. Back-to-school costs are one of the clearest, most seasonal examples of exactly the kind of spending it's designed for. But this applies to all sorts - Christmas, birthdays, holidays, insurance payments - how great would it feel to have the whole year's car insurance sitting there ready to pay?
What a Sinking Fund Actually Is (and Why It's Different From an Emergency Fund)
A sinking fund is money you deliberately set aside, in small regular amounts, for a specific expense you know is coming - even if you don't know the exact date or exact amount yet. It's not a rainy-day fund for the unexpected, it’s really the opposite - it's for the entirely expected.
Your emergency fund is for the boiler that dies without warning. Your sinking fund is for the boiler service you know is due every year, the car MOT, the Christmas presents, and - the one we're focusing on here - the September costs that arrive whether you've planned for them or not. If you're starting completely from scratch, I'd prioritise building a small emergency fund before trying to create ten different sinking funds.
This distinction matters because it changes how you think about the money. An emergency fund sits there, untouched, waiting for a crisis. A sinking fund gets built up specifically to be spent - for a known purpose and probably on a known date. You're not saving in case something happens, but because you already know it will.
Back-to-school costs are about as predictable as spending gets. Term starts the same time every year - kids grow, uniforms wear out, shoes get outgrown, trips get planned. It is genuinely predictable spending, and yet it catches people off guard over and over because most of us never build the fund - we just absorb the cost in the moment and feel slightly sick about it.
The Back-to-School Costs Nobody Actually Budgets For
Before you can build a sinking fund, you need an honest list of what you're actually funding. This is easy to underestimate because most people only remember the obvious bits: uniform (jumpers, trousers, skirts, PE kit), shoes, a school bag, basic stationery.
The costs people might forget until they're staring them in the face: a second pair of shoes because the first pair got wrecked within a fortnight, replacement kit when something goes missing at the bottom of a lost property pile, ‘specialist’ equipment for particular subjects (art supplies, a calculator, cookery ingredients money), school photos for nana, the first school trip of the year, after-school club fees, and - if you've got older kids - technology costs like a laptop, tablet, or the software or subscriptions a school now expects you to have.
Then there's the cost of growth itself. If you've got more than one child, or a child who's had a growth spurt, last year's uniform simply won't do, and you're not just topping up, but starting again close to scratch.
Sit down and actually write this list out, ideally using what you spent last year as your starting point (check bank statements from August and September if you can - it's more revealing than memory). This might be uncomfortable but it’s an essential first step. You cannot build a sinking fund for a number you haven't worked out.
How to Work Out What You Actually Need to Save
Once you've got your list, add it up. Don't round down to make yourself feel better - round up slightly, because there's always something you've forgotten…
Let's say your honest total for one child comes to £250. For two children, maybe it's £420 once you account for some shared costs and some doubled-up ones. Whatever your number is, that's your target.
Now divide it by however many months you've got before the costs land. If you're starting this sinking fund now, in August, for costs that hit hard in the same month - you've missed the ideal window this year, and that's fine, it happens, we're fixing it for next year. But if you're building this fund from, say, January through to August, that's eight months to spread £250 across, which comes to roughly £31 a month. £1 a day. A cost that felt like a poke in the eye in August becomes something you barely notice leaving your account each month.
This is the entire magic trick of a sinking fund: it doesn't reduce what you spend, it just removes the shock of spending it all at once. The cost is identical either way - what changes is whether you feel it as one brutal hit or twelve gentle nudges.
If you've got more than one ‘seasonal ambush’ in your life - Christmas, birthdays, car costs, back-to-school - you can run several sinking funds in parallel, each with its own small monthly amount, each simply doing its job in the background without you having to think about it.
Where to Actually Keep the Money
The best place for a sinking fund is somewhere separate from your everyday spending account, so you're not tempted to dip into it for something else and somewhere you can see it building, so there's a small psychological reward in watching the number go up.
Most UK banking apps now offer some version of ‘pots’, ‘spaces’ or sub-savings accounts you can open directly within your existing bank app (Monzo, Starling, and several of the high street banks all have versions of this) - these are ideal because you can label them clearly (‘Back to School 2027’) and move money in automatically without having to think about it.
If your bank doesn't offer that, a simple separate easy-access savings account works just as well. The key features you want are: easy to set up, easy to automate a transfer into, and slightly annoying to access on impulse - you want a small amount of friction between ‘I fancy that’ and the money actually moving, without making it hard to get to when September actually arrives.
I would add that interest is a nice bonus here, not the point, but if the choice is between two accounts, it’s the obvious answer. You're not trying to grow this money aggressively - you're trying to have it, intact and ready, exactly when you need it. A decent easy-access savings rate is enough, this isn't the pot you're investing.
Automating It So You Never Have to Think About It Again
The single biggest reason sinking funds fail isn't bad maths; it’s relying on willpower, especially over the longer term. If moving the money each month depends on you remembering, and choosing to do it, and having enough left over that particular month, it will eventually not happen. Not because you're bad with money, but because that's just how life works.
Set up a standing order for the day after payday, for the exact monthly amount you calculated, moving straight into your labelled pot or account. Treat it exactly like a bill - because functionally, that's exactly what it is. You are simply paying September's bill in twelve small instalments instead of one big fat one.
If your income is variable - if you're self-employed, freelance or your hours change month to month - automate a percentage rather than a fixed amount, or set a lower ‘baseline’ automated amount and top it up manually in stronger months. The goal isn't ever perfection but simply consistency. Maybe you’re aiming for £420 but you manage £350 by next September - how much better does it feel to be searching for £70 than £420?
If You're Starting Late (or From Zero) This Year
If you’re reading this in August, with September already breathing down your neck, you probably don't have time to build the whole fund this year, but that's fine, we're fixing it for next year! Your job, if this sounds like the sort of thing that would make your life 100% less chaotic, is to keep a note of the costs this year so that you have an accurate starting point for next year's sinking fund, set up in good time, so this is the last year it catches you out.
Making This a Habit, Not a One-Off Fix
The real win here isn't September specifically - but building a small, repeatable system that absorbs a predictable cost every single year without any drama. Once back-to-school has its own sinking fund running in the background, you can do exactly the same thing for Christmas, for car costs, for birthdays, for anything in your life that arrives on a schedule but somehow still manages to surprise you.
I cannot tell you how delightful it feels to just have the money there when you need it - after having been a person that scrambles and faffs around. It’s great to have the money, and no stress, but it’s incredible to be the sort of person that has thought of the thing and sorted it well in advance.
Money stress isn't always about not having enough. Sometimes it's simply about timing - the gap between when a cost lands and when you're prepared for it. That’s called cash flow in a business and it matters just as much for us. Sinking funds close that gap without requiring you to earn more, cut back harder or become a different kind of person with money. It just asks you to be a little bit more honest, a little bit earlier, about what's coming.
September will come again next year. It always does. The only question is whether you'll be ready for it, or doing this same panicked scramble all over again.
Your 10-minute sinking fund setup
Check what you spent last August/September.
Add 10% for price rises and forgotten costs.
Decide when you want the money ready.
Divide the total by the number of paydays.
Set up the automatic transfer.
Name the pot.
If you're reading this and thinking, ‘I know what I should be doing with my money, so why do I find it so hard to actually do it?’ - that's exactly the sort of thing I work on in my money coaching.
We can look at the practical stuff - budgeting, saving, investing, pensions - but also the habits, emotions and money stories underneath it. Because sometimes you don't need another spreadsheet - you need to understand why money keeps feeling harder than it should.
If you'd like some help getting your money feeling calmer, clearer and more under control, you can book a money coaching session with me here.
Love Eleanor xxx
P.s. If you're in England, from September 2026, schools will be limited in the number of branded uniform and PE kit items they can require you to buy. Schools should also make second-hand uniform available, so check your school's uniform policy before you start shopping.
