Why starting at 25 beats starting at 35
Your money can make money. And then that money makes money too. It sounds small — but over time, it's the difference between tens of thousands of pounds. Here's what it looks like.
Here's the basic idea: you save some money. It earns a return. Next year, that return earns its own return. And the year after that, you're earning returns on your returns on your returns. Your money starts making money by itself — and the longer you leave it, the faster it grows.
That's compound interest. It sounds almost too simple to matter, but it's the single most powerful thing in personal finance. And the thing that makes it work isn't being clever with investments — it's just time.
The 10-year head start
Example
Based on Sam, 28, earning £38,000/year, investing £200/month in a Stocks & Shares ISA.
Two people invest exactly the same amount every month — £200. Same fund, same returns. The only difference: one starts at 25, the other waits until 35.
By 65, the person who started at 25 has £306,815. The person who started at 35 has £169,826. That's a gap of £136,989 — not because they invested more, but because their money had 10 extra years to compound.
£200/month invested at 5% average annual return
Illustrative projection only. Uses a 5% average annual return after fees, which is not guaranteed. Your actual returns may be higher or lower. The value of investments can go down as well as up.
Why the gap is so big
The person who started at 25 put in a total of £98,400 of their own money. The person who started at 35 put in £74,400. That's only £24,000 more in actual contributions — but it produced £136,989 more in total value.
The extra growth isn't coming from the extra contributions. It's coming from compound returns on the early years — the returns that had the longest time to snowball.
This is why the best thing most people in their 20s can do with their money isn't picking the perfect fund or trying to time the market. It's just starting. Even a small amount. Even if it feels like it won't make a difference. The maths does the heavy lifting — you just need to give it time.
What this means in practice
You don't need a big salary or a lump sum to get started. £100 a month into a Stocks & Shares ISA from age 25, left alone for 40 years at 5% average returns, grows to roughly £153,000. You'd have put in £48,000 of your own money. The other £105,000? That's compound interest doing its thing.
Look — nobody ever feels “ready” to start investing. But every year you wait, you're not just missing out on that year's savings. You're missing out on decades of growth on those savings. That's the bit that hurts.
Quick rule of thumb: at 5% growth, your money roughly doubles every 14-15 years. So £1,000 invested at 25 becomes ~£2,000 by 40, ~£4,000 by 55, and ~£7,000 by 65. That same £1,000 invested at 35 only makes it to ~£3,500 by 65.
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