How Much to Save for Retirement at Every Age
Benchmarks by age, what they assume, and the arithmetic of catching up. Starting at 25 needs $351 a month for a target that costs $1,252 a month if you start at 45.
Compound Interest, Explained With Real Numbers
$200 a month for 30 years at 7% becomes about $244,000, of which only $72,000 came from you. The other $172,000 is the reason time matters more than the amount you invest.
The short version
- Compounding means your returns start earning returns. The effect is small early and dominant late.
- $200 a month at 7% for 30 years reaches about $244,000 — $72,000 of it your money, $172,000 growth.
- Starting ten years earlier roughly doubled the outcome in our example, on only $36,000 more contributed.
- Compounding works identically against you on debt, which is why a 24% card is so destructive.
Compound interest is described as magic so often that the actual mechanism gets lost. There is no magic. There is one rule, applied repeatedly: you earn returns on your returns, not just on what you put in.
Simple interest on $1,000 at 7% pays $70 every year forever. Compound interest pays $70 in year one, then $74.90 in year two — because you now have $1,070 working, not $1,000. The gap looks trivial. Over decades it is the entire story.
What it looks like over time
Take someone investing $200 a month, earning 7% a year — roughly the long-run average annual return of a diversified global equity portfolio, before inflation and with no guarantee it repeats.
| After | You put in | Balance | Growth | Growth as % of balance |
|---|---|---|---|---|
| 10 years | $24,000 | $34,600 | $10,600 | 31% |
| 20 years | $48,000 | $104,200 | $56,200 | 54% |
| 30 years | $72,000 | $244,000 | $172,000 | 70% |
| 40 years | $96,000 | $525,000 | $429,000 | 82% |
Look at the last column. In the first decade you are doing most of the work. By year 30, seven dollars in every ten came from growth rather than from you. By year 40, more than eight.
Now look at the balance column differently. Between year 30 and year 40, the balance rises by $281,000 — while you contributed $24,000. The last decade generated more than the first three combined.
Why the last years matter most
Growth in any year is proportional to the balance you already hold. A 7% return on $30,000 is $2,100. The same 7% on $400,000 is $28,000. This is why leaving a portfolio alone for the final stretch is worth more than any amount of cleverness at the start — and why withdrawing early costs far more than the amount withdrawn.
Time beats amount
The most important variable is not how much you invest. It is how long the money compounds.
Two people, both investing $300 a month at 7%, both stopping at 65:
| Starts at 25 | Starts at 35 | |
|---|---|---|
| Years invested | 40 | 30 |
| Total contributed | $144,000 | $108,000 |
| Balance at 65 | $787,000 | $366,000 |
An extra $36,000 of contributions produced an extra $421,000. The ten years at the beginning were worth more than everything the later starter did across three decades, because those early contributions had forty years to compound rather than thirty.
The practical implication is not "you have already missed it" if you are 40. It is that the best day to start was earlier and the second best is now — and that the gap widens every year the decision is deferred.
The rule of 72
A useful mental shortcut: divide 72 by the annual return to get the approximate number of years for money to double.
- At 7%: 72 ÷ 7 ≈ 10.3 years to double.
- At 3%: 24 years.
- At 10%: 7.2 years.
So $10,000 invested at 7% becomes roughly $20,000 after ten years, $40,000 after twenty, $80,000 after thirty. (The precise figures are $19,672, $38,697 and $76,123 — the approximation drifts a little, but it is close enough for mental arithmetic.)
The rule works in reverse too. At 3% inflation, prices double in 24 years — which is why holding a retirement pot entirely in cash for decades is riskier than it feels.
Compounding in reverse
The same mechanism runs against you on debt, and faster, because consumer credit rates are far higher than realistic investment returns.
A $5,000 credit card balance at 22% compounds monthly. Pay $100 a month and you will pay $8,678 in interest over eleven years — more than the original balance, because in the early months almost the entire payment goes on interest and the principal barely moves. The full arithmetic is in the real cost of minimum payments.
This is why the order of operations puts high-rate debt ahead of investing. Clearing a 22% debt is a guaranteed 22% return. No investment offers that with certainty.
The assumptions, stated plainly
Every number above rests on assumptions, and honest ones are worth stating:
- 7% is an average, not a schedule. Real markets deliver +22% one year and −18% the next. The average emerges over decades; no individual year resembles it.
- These are nominal returns. At 3% inflation, $244,000 in thirty years has the purchasing power of roughly $100,000 today. That is still a substantial result, but it is not the same number.
- Fees are excluded. A 1% annual charge does far more damage than it sounds — see how fees compound, where the same example loses about $96,000.
- Tax is excluded. Returns inside a pension or tax-free wrapper compound untaxed; in a taxable account they do not.
- Past returns are not a forecast. The historical average is evidence about a range of outcomes, not a promise about yours.
What this actually implies
- Start now, at whatever amount is possible. $50 a month starting today beats $200 a month starting in five years for a long horizon.
- Automate it. A standing order on payday removes the monthly decision, and the monthly decision is where consistency dies.
- Leave it alone. The largest gains happen in the final years. Withdrawing early does not cost you the withdrawal, it costs you everything that amount would have become.
- Keep costs low. Fees compound in exactly the same way as returns, in the opposite direction.
- Raise contributions with income. Half of every pay rise into investments is painless, because you never adjusted to having it.
Common questions
Is 7% a realistic return to assume?
It is a common planning assumption for a globally diversified equity portfolio before inflation, based on long-run historical averages. It is not a guarantee and it is not what any single year will deliver. Many planners use 5–6% for a more conservative projection, or work in real terms — around 4–5% after inflation. Run your own numbers at more than one rate and note how much the answer moves; that sensitivity is itself useful information.
Does compounding work in a savings account too?
Yes, mechanically it is identical — interest is added to the balance and then earns interest itself. The difference is the rate. At 4%, money doubles in about 18 years before tax, and inflation may consume most of that gain. Cash is the right home for money you need within a few years; it is a poor engine for thirty-year compounding.
I am 45 with nothing invested. Is it too late?
No, but the plan has to be different. With twenty years rather than forty, contributions do more of the work and growth does less, so the realistic levers are a higher savings rate, a later retirement date, and keeping costs down. Twenty years is still long enough for compounding to matter substantially — $500 a month at 7% for twenty years is around $260,000.