“When can I retire?” might be the most-asked and least-answered question in personal finance. Least-answered because the honest response is a probability cloud — markets, inflation, health, tax rules — and clouds don’t fit in a sentence. So most people never get past vaguely hoping it’s before 70.
Here’s the reframe that makes it buildable: stop asking when you can retire and ask when could the pot cover the life I actually live? That’s not a cloud. That’s four numbers and a copy-down — the same machinery as the compound growth tracker, pointed at the other end of the journey.
The usual honesty: this is a model for seeing the shape of your future, not financial advice. Before acting on what it shows you, that’s a conversation for a regulated adviser.
The four numbers
- Pot today — everything earmarked for retirement: pensions
(check the apps you’ve been ignoring), ISAs if you intend them
for this. Name the cell
pot_now. - Monthly contribution — yours plus your employer’s, gross.
Name it
monthly_in. - Real growth rate — the long-run assumption after inflation.
Working in real terms is the trick that keeps the model honest:
a cautious 3–4% real means every figure the model produces is in
today’s money, and “£2,000 a month” still means something.
Name it
growth. - The life you’re paying for — your essential monthly spend, in
today’s money. If you built
the four-number budget,
you already know it. Name it
monthly_need.
The target the pot has to hit
A pot can’t just equal your spending — it has to survive being spent from, through crashes, for decades. The rough-and-honest convention is a safe withdrawal rate of about 4% a year (many people prefer 3.5% for early retirement — the model makes changing it trivial). Which flips into the memorable version:
target = monthly_need × 12 / 4% (= 25 years of spending)
Needing £1,800 a month? 1800 × 12 / 0.04 = £540,000 in today’s
money. Yes, that number is big. Two softeners before you close the
tab: the state pension (~£12,000 a year from your late 60s,
verified in two minutes at gov.uk’s forecast page) can be modelled
as reducing monthly_need from state pension age — it typically
knocks a third or more off the target. And every £100 you can
trim from essential spending cuts the target by £30,000. Frugality
is leverage here, not virtue.
The countdown table
One row per year. Three formulas, copied down:
| Column | Formula (row 2) |
|---|---|
| Year | =YEAR(TODAY())+ROWS($A$2:A2)-1 |
| Pot | =B2*(1+growth) + monthly_in*12 |
| Target | =monthly_need*12/0.04 |
Start the Pot column with pot_now, copy down forty rows, and read
down until Pot first exceeds Target. That row is your answer —
or as a formula:
=INDEX(Years, MATCH(TRUE, Pots >= Targets, 0))
Now interrogate it
A date on a chart changes the questions you can ask. Because the inputs are named cells, each what-if is a ten-second edit:
- Contributions: what does £100 more a month do to the crossing year? (For most people mid-journey: more than they expect.)
- Growth: drag it from 3% to 5% and watch how much the answer swings — that swing is the honest uncertainty, on one screen.
- The life: model
monthly_needdropping at state pension age, or a smaller “semi-retired” number from some earlier year. The question quietly shifts from “when can I stop?” to “when could I afford to work less?” — often a decade sooner, and often the better question.
The model’s real product isn’t the date — the date will move. It’s the sensitivity: learning which lever is yours to pull. Spending is usually the strongest one, which is exactly what the budget measures.
A probability cloud you can’t look at becomes a curve, a line, and a crossing. Excel’s whole job, really: turning dread into arithmetic.