How long it takes to reach £100,000

£100,000 is the first number in British money that feels like it means something. It is far enough away to need a plan and close enough to reach on an ordinary salary, which is why it is the figure people actually ask about. The trouble is that almost every answer you will find to the question is a third too short, and for a reason nobody mentions.

What the arithmetic says

Three standing orders, no starting balance, 5 per cent growth a year and 3 per cent inflation. The same engine that runs our calculator, asked the same question three times:

The second column is the one worth sitting with.

The gap between the two answers

At £200 a month the balance crosses £100,000 after 22 years and 10 months. That is the number every other calculator will give you, and it is true in the narrow sense that the screen will one day say £100,000.

It is also close to meaningless. £100,000 in 2049 is not £100,000. At 3 per cent inflation it buys roughly what £50,000 buys today — so the pot that finally reads six figures is worth about half of what you were picturing when you set the standing order up. To have £100,000 of today's spending power, at £200 a month, takes 43 years and 8 months. Nearly double.

That gap is not a rounding error or a pessimistic assumption. It is what happens when a small contribution has to outrun inflation for a long time, and it is the single most useful thing this calculation can tell you. Showing only the cash figure is the most flattering thing a calculator can do, so ours shows both and treats the real one as the answer.

The gap also closes fast. At £500 a month it is five and a half years rather than twenty-one. At £1,000 a month it is under two. Inflation punishes slowness specifically, and the longer the journey the more of it is spent standing still.

The part that works the other way round

Look at the last two columns and something inverts.

The person saving £200 a month pays in £54,800 and lets growth find the other £45,671 — a little over 45 per cent of the pot is investment return rather than their own money. The person saving £1,000 a month pays in £85,000 and gets just £16,331 of growth, around 16 per cent.

So the slow saver's money works much harder, and still arrives too late to be worth what they wanted. Both things are true at once, and holding them together is most of what understanding compounding actually means. Time is what produces growth; contributions are what buy the deadline. If you have time, growth will do a surprising share of the work. If you do not, no rate of return available to an ordinary investor will rescue a contribution that is too small — you have to put more in.

This is also why the advice to "start early" is worth more than it sounds and less than it is usually sold as. Starting early genuinely does hand the work to compounding. It does not make £200 a month into a plan for £100,000 in a decade, and no amount of starting early will.

Where the money sits while it does this

None of the figures above account for tax, and at these amounts they mostly do not need to. £20,000 can be paid into ISAs in the 2026 to 2027 tax year, which is more than £1,000 a month, so every column in that table fits inside a wrapper where growth and withdrawals are untaxed. For most people aiming at £100,000, the tax question is answered simply by using the allowance.

One wrinkle is worth knowing if you are saving for a first home. A Lifetime ISA takes £4,000 a year and adds a 25 per cent government bonus, up to £1,000 — and that £4,000 counts towards the same £20,000 limit. On the £200 a month row, £2,400 a year, the bonus is worth £600 a year for doing nothing, which moves the arithmetic more than any plausible difference in investment return would. It is also restricted: you must open one before 40 and pay in before 50, and taking the money out for anything other than a first home or reaching 60 carries a charge that can leave you with less than you put in.

What these numbers assume, and what they are not

The 5 per cent is an assumption, not a forecast. Nobody knows what the next twenty years return, and a piece that presents a growth rate as a fact is doing the same thing as a calculator that hides inflation. Change it in the tool and watch what moves — the honest finding is that the durations are far more sensitive to what you pay in than to what you assume about returns, which is the opposite of how most people spend their attention.

Two smaller choices are worth stating. Contributions are counted at the end of each month, after that month's growth, which is the conservative convention. And the annual rate is converted to its true monthly equivalent rather than divided by twelve — dividing by twelve quietly turns a 5 per cent assumption into slightly more than 5 per cent, and over forty years that is not nothing.

None of this accounts for your income tax position, your pension, or what else the money might be needed for. It is arithmetic about one pot, not a plan.

Run it on your own numbers

The table above is three rows from a much larger picture, and yours will not be any of them. Our time to £100,000 calculator takes your starting balance, your monthly amount and your own assumptions, and gives you both answers side by side — the cash one and the real one.

If the real answer comes back further away than you expected, that is the calculation working. It is a better thing to find out now, while the standing order is still adjustable, than in twenty years. And if you are making a decision that turns on any of this — a pension, a property, a large sum moving at once — take it to a regulated financial adviser who can see your whole position, not a table on a website.