Every year contains the same ambushes. Car insurance lands in March, the MOT and its repairs in June, Christmas in December — and each one arrives with the same little lie attached: “this is an unusually expensive month.” It isn’t. It’s a completely usual month in a system with bad rhythm: costs that occur yearly, colliding with a budget that thinks monthly.
The four-number budget gets wobbled by exactly these hits, and the classic patch — raiding the emergency fund — is wrong on principle: the MOT is not an emergency, it’s an appointment. The proper tool is older than spreadsheets, and it’s called a sinking fund: money set aside monthly, in advance, toward a known future bill. Excel makes it a ten-row table.
The table
One row per annual (or irregular) cost, in a proper Table:
| Item | Annual cost | Due month | Monthly slice |
|---|---|---|---|
| Car insurance | £680 | Mar | =[@Annual]/12 |
| MOT + servicing | £420 | Jun | £35 |
| Christmas | £600 | Dec | £50 |
| Home insurance | £310 | Sep | £26 |
| TV licence | £170 | Apr | £14 |
| Total | £2,180 | £182 |
That bottom-right number is the entire product: £182 a month is what your “annual surprises” actually cost. Not zero in the good months and £680 in March — £182, every month, as fixed as rent. Move that amount to a separate savings pot by standing order on payday, pay every annual bill from the pot, and the expensive month ceases to exist as a category.
The two refinements that make it real
Mid-year starts need a catch-up column. Start in July with
insurance due in March: eight months to save £680 means £85/month
until the renewal, then it relaxes to £57.
EOMONTH and a little date maths
compute months-remaining; =[@Annual]/months_left does the rest.
The first year is the steep one — every year after, you’re the
person for whom renewal quotes are boring.
Check the pot against the calendar. A second worth-it column: cumulative-due versus cumulative-saved, and a conditional-formatting spotlight on any month where the pot would run dry. Christmas in December and insurance in March both being fully funded depends on the order the bills land — the sheet sees the collision in July; your bank balance would have discovered it live.
Why this beats “being careful”
The sinking fund isn’t a savings technique, it’s an information technique. The £182 was always being spent — the table just moves the knowledge of it from December-you (panicking) to January-you (planning). And it upgrades the rest of the system: the runway’s crisis floor becomes honest because annual costs are now in it pro-rata; the emergency fund stops being raided for appointments and goes back to guarding against genuine surprises; and renewal season turns adversarial in your favour — with the pot already full, the insurance renewal isn’t a crisis to accept but a quote to shop.
It also quietly deletes the most corrosive money feeling there is: being behind. You can’t be behind on a bill you’ve been paying yourself for eleven months.
Ten rows, one division, one standing order. The expensive month was never expensive — it was just poorly scheduled, and scheduling is a solved problem in a spreadsheet.