How Much to Save for Retirement: Key Inputs

"How much should I save for retirement?" has no single answer, because the result depends on a handful of assumptions that nobody can know in advance: the return your savings will earn, how fast prices will rise, how long you will contribute and how much you will draw down each year. What you can do is see how sensitive the answer is to each one. This guide walks through the inputs of the Retirement Savings Calculator, uses one base case throughout, and changes a single input at a time so you can see which ones matter most. All amounts are in a generic currency, so they apply wherever you live.

The inputs and what each one does

• Current age and retirement age set how many years your money has to grow. This is the most powerful input, because growth compounds.
• Current savings is what you already have set aside for retirement.
• Monthly contribution is what you add each month, kept level in the projection.
• Expected annual return is the average yearly growth you assume. It is an assumption, not a promise.
• Expected inflation does not change the size of your pot. It changes what the pot can buy, so it is used to restate results in today's money.
• Withdrawal rate is the share of the pot you plan to take each year once you retire.

The base case

You are 35, plan to retire at 65, have 20,000 saved and add 800 a month. You assume a 6% annual return, 2.5% inflation and a 4% withdrawal rate. Over 30 years you contribute 308,000 in total, and the projection gives:

• Savings at retirement: 924,063.54.
• The same pot in today's money: 440,540.53.
• A 4% withdrawal in the first year: 36,962.54, which is 17,621.62 in today's money.
• That is roughly 1,468.47 a month in today's money.

Notice the gap between the first and second numbers. After 30 years of 2.5% inflation, the large future figure is worth less than half as much in today's terms. Planning against the nominal number alone is the most common way to overestimate a retirement pot.

Sensitivity: change one thing at a time

Each table below changes one input from the base case and leaves the rest alone. The last column is the yearly income at a 4% withdrawal in today's money (except in the withdrawal table, where the rate itself changes).

Expected return

Two percentage points either way moves the outcome by roughly a third down or more than half up. Because nobody knows the long-run return in advance, it is sensible to run a low case as well as a hopeful one, and to plan around the cautious figure.

Inflation

The nominal pot stays at 924,063.54 in all three rows. Only its purchasing power changes. A full percentage point of extra inflation over three decades removes about a quarter of the pot's real value. You can explore the effect of price rises on any amount with the Inflation Calculator.

Monthly contribution

Every extra 200 a month adds a steady 200,903.01 or so to the final pot, since the contribution part of the calculation is linear. This is the input you control most directly.

Retirement age

Working five years longer does three things at once: more contributions, more years of growth and a shorter retirement to fund. That is why the pot grows by far more than the extra 48,000 contributed.

Withdrawal rate

The 4% figure is a rule of thumb that came out of studies of historical US market returns, not a guarantee. A lower rate leaves more margin if returns disappoint or you live a long time, and a higher rate risks running the pot down sooner. It also assumes you start drawing at retirement, so your own start age and length of retirement matter.

Starting earlier or later

With everything else unchanged, starting at 25 instead of 35 gives 1,812,341.66 at retirement on 404,000 contributed, or 674,971.54 in today's money. Starting at 45 gives 435,836.81, which is 265,978.54 in today's money, on 212,000 contributed. Ten years of extra growth is worth more than ten years of extra contributions.

What the projection assumes and leaves out

• One constant return. Real returns swing from year to year, and a bad run just before or after you retire does much more damage than the same average spread evenly. This is called sequence-of-returns risk and a single-rate projection cannot show it.
• Level contributions. Most people raise contributions as their income grows. The projection does not.
• No tax, fees or employer contributions. Fees reduce your effective return, and employer matches, state pensions or other income can reduce how much you need to save yourself.
• Your spending, not a formula. The right target is what you expect to spend in retirement, which depends on housing, health and where you live.

Using this to plan

A practical approach is to decide the yearly income you want in today's money, run the calculator with a cautious return and a higher inflation figure, and adjust the monthly contribution or retirement age until the result reaches it. If you already have a target pot in mind, the Savings Goal Calculator works backward to the monthly amount required. For how compounding builds the pot over time, see the guide on compounding frequency and the explanation of what a regular-investment projection does and does not promise in SIP Projections Explained. None of this is personal financial advice, so check the rules for your own country's pension and tax system.