How Much Do You Need to Retire?
The 4% Rule Isn't Your Answer

Ask the internet how much you need to retire and you get one number: 25 times your annual expenses. Spend 60,000 a year, retire on 1.5 million. Clean, memorable, endlessly repeated.

It comes from the 4% rule, and it is a genuinely useful piece of research. But it is not a universal answer, and almost nobody quoting it mentions what it assumes. Run the maths backwards and the 4% rule implies your money earns just 1.2% a year above inflation for thirty years — a deliberately pessimistic figure, chosen so the number survives the worst market history on record.

If your assumptions differ — and they almost certainly do — your multiple is not 25. This guide shows where the rule comes from, what it hides, and how to work out the number that actually applies to you.

Where "25× Your Expenses" Comes From

In the 1990s, financial adviser William Bengen tested every 30-year retirement window in US market history and asked a simple question: what is the highest percentage you could withdraw in year one, then raise with inflation each year, without ever running out?

His answer was 4.15%, which everyone who repeated it promptly rounded down to 4%. Flip that around and you get the multiple we all know:

The important word in Bengen's research is survived. He was not describing the typical outcome. He was looking for a rate that held up even if you retired at the worst possible moment — straight into a crash followed by high inflation. That is a safety standard, not a forecast.

What the 4% Rule Quietly Assumes

Here is the part that rarely gets said out loud. A corpus that funds a rising expense for a fixed number of years has a precise mathematical value — so you can work backwards and ask what steady return 25× is equivalent to.

The answer is about 1.22% a year above inflation, sustained for 30 years.

Bengen never stated that figure — his method was historical simulation, not a fixed return — but it is what the multiple works out to. And it is extremely conservative. It is not a forecast of weak markets; it is roughly what you would have earned in the worst stretch history has on record. If you expect to beat 1.22% above inflation, which most balanced portfolios have managed over long periods, then 25× overshoots what you actually need — sometimes by a wide margin.

Inflation Hits You Twice

Most people underestimate their number for one reason: they think about inflation once, when it actually applies in two separate places.

First, before you retire. The lifestyle you have today costs more every year until you stop working. At 3% inflation, expenses of 3,000 a month today become 7,282 a month in 30 years:

That is compound interest — the same formula a compound interest calculator uses to grow your savings, except here it is working against you, on prices.

Second, all the way through retirement. Prices do not freeze on your last working day. That 7,282 keeps climbing for every one of your retirement years, so your corpus has to fund a rising bill, not a flat one.

This is why "I spend 3,000 a month, so I need 3,000 a month" is the most expensive mistake in retirement planning. The real target is more than double, before you have accounted for a single year of retirement.

The Real Rate Decides Everything

Once you accept that expenses rise throughout retirement, one number does most of the work: the real rate of return — what your corpus earns after inflation is stripped out.

Note that it is a ratio, not a subtraction. A 7% return with 3% inflation is not a 4% real rate — it is 3.88%. Small difference on paper, meaningful over decades.

Your corpus then has to cover the full stream of rising expenses:

That bracketed term is your multiple. The 4% rule fixes it at 25. In reality it moves with just two inputs — your real rate, and how long you expect retirement to last.

Your Multiple Probably Isn't 25

Here is what the multiple actually looks like across a realistic range. Read it as "corpus equals this many times your first-year retirement expenses":

Two things jump out. Retiring earlier lengthens retirement and pushes the multiple up — 35 years needs more than 30. And the real rate matters more than almost anything else: holding the length at 30 years, moving from 1.22% to 4% real cuts the requirement by nearly a third.

Working Out Your Own Number

You only need six inputs, and you already know most of them.

1. Open the Retirement Calculator and pick your currency.
2. Enter your current age, the age you want to retire, and a life expectancy. Plan for 85–90 rather than an average — running out of money is a far worse error than saving slightly too much.
3. Enter your current monthly expenses in today's money. Do not try to inflate them yourself; the calculator does that.
4. Set your inflation assumption — around 2–3% for the US and Europe, 5–6% for India.
5. Set two return rates: one for the years you are still investing, and a lower one for retirement, when most portfolios turn conservative.
6. Add anything you have already saved. It grows until retirement and reduces what you still need to put aside.

The result gives you three things: what your lifestyle will cost per month when you retire, the corpus that funds it, and the monthly saving that gets you there.

That last figure is a monthly investment running for decades, so if you want to test it on its own — a different amount, a different return, a shorter horizon — the SIP Calculator projects any monthly contribution forward and shows the year-by-year split between what you put in and what compounding added.

Then re-run it once a year. Your expenses change, your income changes, and markets rarely match the smooth average any calculator assumes. A retirement number is not a one-time calculation you file away — it is an estimate you keep correcting as the facts arrive.