There is one chart that changes how people save: the line showing what they put in, and the second line showing what the money became. The gap between them is compounding — interest earning interest — and no paragraph about it persuades anyone. The chart does.

Banks won’t draw it for you. Excel will, in one small table and three formulas. (Arithmetic and spreadsheet craft, not financial advice — growth rates here are assumptions you choose, not promises.)

The engine: one row per year

Start a Table with Year | Paid in | Value. Three inputs live above it in named cells: monthly (say £200), rate (say 5% a year — your assumption, be modest), and that’s it.

Paid in — what you’ll have contributed by the end of each year:

=monthly * 12 * [@Year]

Value — last year’s value, grown one year, plus this year’s contributions grown roughly half a year (they arrive monthly, so on average they’re invested for six months):

=B2 * (1 + rate) + monthly * 12 * (1 + rate/2)

Copy down 30 rows. That half-year adjustment is the honest touch most quick calculators skip, and it’s one multiplication.

The chart that does the arguing

Select the Table, insert a line chart, two series: Paid in and Value. Format honestly — start the axis at zero.

years → the gap = compounding Value Paid in
Straight line: your effort. Curve: your effort plus time. The shaded gap needs no caption at the dinner table.

Early on, the lines hug — this is why people quit saving in year two. Around year ten they visibly part, and by year twenty the gap is often bigger than everything you paid in. Same £200 a month all along; the only ingredient that changed is time. Seeing that curve for your own numbers is worth more than any finance article, including this one.

Make it yours

  • Track reality against the plan. Add an Actual column and, once a year, type in the real balance from your ISA or pension statement. Plan versus reality on one chart is the entire personal-finance feedback loop in one picture. (UK note: an ISA’s £20,000 annual allowance means the tracker doubles as a “room left this year” check — one extra SUMIFS if you log contributions in a budget-style Spend table.)
  • Ask “what if” properly. Because monthly and rate are named input cells, questions cost nothing: £250 instead of £200? 4% instead of 5%? Change one cell and the whole curve redraws. That’s the modelling habit — inputs in named cells, formulas everywhere else — that separates a calculator from a toy.
  • Play the sequences. Duplicate the Value column at 3% and 7% and you’ve drawn a fan of futures: modest, expected, lucky. Planning on the middle line while seeing the lower one is what “realistic assumptions” actually looks like.

The Excel lesson hiding in the money lesson

Notice what this file is: named inputs, one Table, one recursive formula, one honest chart. No macros, nothing clever. The most persuasive spreadsheets are usually the simplest ones pointed at a question you actually care about — and few questions focus the mind like what will my money be doing in 2046?