Retirement planning: compounding and inflation
Retirement is paid for by savings that grow over decades, and by prices that also rise over decades. This lesson separates the two. It shows how a monthly contribution compounds, why the real return after inflation is what counts, how losing ten years of saving costs more than ten years of contributions, and how a pot is turned into a yearly income. It reads Federal Reserve survey data on US retirement accounts and the average Social Security retirement benefit. A calculator moves the contribution, the return, inflation and the number of years.
- Level
- Beginner
- Reading time
- About 26 minutes
- Know this first
- Insurance fundamentals
By the end you will be able to:
- explain how regular contributions compound over decades
- convert a future balance into today's dollars and say why it matters
- work out the real return from a nominal return and inflation
- turn a retirement balance into a yearly income over a set number of years
- see why starting later costs more than the missed contributions
Paying for a second career of not working
For most people, retirement means living for decades on money saved earlier. Two forces act on that money over the same decades, and they pull in opposite directions. Compounding makes savings grow, because returns are earned on earlier returns. Inflation makes each dollar buy less, because prices rise. A plan that watches only the first force will look better than it is.
This lesson builds on the earlier lessons on compound interest and inflation, and on annuities, which show how a pot is turned into a stream of payments. It uses a calculator in which a worker saves a fixed amount each month for a number of years, and then lives on the pot for thirty years. It also looks at what the Federal Reserve’s survey says US families hold in retirement accounts, and what the average Social Security retirement benefit is.
Contributions that compound
Suppose a person saves a fixed amount every year. Each contribution earns a return, and that return earns a return in the following years. The result is not a straight line. The early contributions have the longest to grow, so they end up contributing far more than their share. A contribution made 35 years before retirement has 35 years of growth. One made in the last year has none.
The growth is also what lets a pot end up larger than everything put in. At a 6% return and 3% inflation, $500 a month for 35 years puts in $210,000 in today’s dollars and leaves $356,691. The rest, $146,691, is growth. The longer the saving, the larger that share.
The real return
A 6% return sounds like 6% more purchasing power each year. It is not. If prices rise 3% a year, the money grows 6% but each dollar buys 3% less. The growth in what the money can actually buy is the real return.
The real return is slightly less than the plain difference of 6% less 3%, because the two effects compound together. When the real return is positive, buying power grows. When it is zero, savings only keep pace with prices. When it is negative, savings buy less each year even though the balance rises. The calculator works in today’s dollars throughout, and also shows the balance in the money of the day, which looks much larger and is much less useful. A balance of $1,003,678 in 35 years’ time sounds like a fortune, but it is the same as $356,691 today.
From a pot to an income
A balance is only useful when it is turned into spending. If the pot is to be used up over a fixed number of years, with the rest of it still earning the real return, the yearly amount it can pay is the level annuity payment for that number of years at the real return, the same calculation as in the lesson on annuities. In the calculator the pot has to last 30 years, and the amount is withdrawn at the end of each year. If the real return is zero, the pot is simply divided by 30.
This lesson uses a target income of $40,000 a year in today’s dollars. The figure is invented, to give something to compare with. It is not a recommendation, and what a person needs depends on where they live, their health and their housing.
What households have and what the benefit pays
The Federal Reserve’s 2025 Survey of Consumer Finances found that 54.9% of US families held a retirement account, against 54.3% in 2022. Among families that held one, the median balance was $106,000, up from $95,200, in 2025 dollars. A median is the middle family, so half had less. The survey also reports the mean balance for families with an IRA or a defined contribution plan, by age.
| Age of reference person | 2022, $ thousands | 2025, $ thousands | Change |
|---|---|---|---|
| Under 35 | 53.8 | 48.4 | −10% |
| 35 to 44 | 154.8 | 182.4 | +18% |
| 45 to 54 | 342.7 | 415.8 | +21% |
| 55 to 64 | 588.5 | 670.2 | +14% |
The mean rises with age, as the compounding argument would suggest, from about $48 thousand for families under 35 to about $670 thousand for those aged 55 to 64. For families under 35 the mean fell from 2022 to 2025. The source does not say why. Means are pulled up by a few large balances, which is why these figures sit well above the $106,000 median. The two measures describe slightly different groups of families, so they should not be compared exactly.
Retirement income for most US workers also includes Social Security. In June 2026 the Social Security Administration was paying 54.62 million retired workers an average of $2,084.40 a month, which is about $25,013 a year (calculated by multiplying by 12). That is 62.5% of the invented $40,000 target. It is an average, so individuals receive more or less, and it is not part of the calculator. The calculator shows what the savings alone can pay.
Build the pot
The worker saves from nothing. The contribution rises with prices, so it stays the same in today’s dollars. Set the monthly amount, the nominal return, the inflation rate and the number of years of saving. The calculator shows the balance at retirement in today’s dollars and in future money, how much of it was put in and how much is growth, the real return, and the yearly income the balance can pay for 30 years.
Saving $500 a month, rising with prices, for 35 years at a 6% return and 3% inflation leaves $356,691 in today’s dollars at retirement, which is $1,003,678 in the money of the day. Of that, $210,000 is what was put in, and growth adds $146,691. The real return is 2.91%. Spread over 30 years, the balance supports $17,993 a year in today’s dollars, 44.98% of a $40,000 target.
Four experiments. First, leave the starting settings alone. The pot is $356,691 in today’s dollars, $1,003,678 in the money of the day, and it supports $17,993 a year for 30 years, 44.98% of the target. Second, set inflation to 0%. The real return rises from 2.91% to 6.00%, the pot becomes $668,609 and the income $48,574, which is 121.43% of the target. The same contributions and the same 6% return go much further when prices are not rising. Third, return inflation to 3% and cut the years of saving from 35 to 25, as if starting ten years later. Contributions fall by 29%, from $210,000 to $150,000, but the pot falls by 39%, to $216,263, and the income to $10,909, 27.27% of the target. The lost years were the ones with the most time to grow. Fourth, return to 35 years and double the saving to $1,000 a month. The pot is exactly double, $713,381, and the income $35,986 is 89.97% of the target. In this model, a balance is proportional to the contribution, so the amount saved and the years saved are the two things that matter most, along with the real return.
What this lesson leaves out
- A single steady return. The calculator assumes the same return and inflation every year. Real returns vary a great deal, and the order of good and bad years matters, especially near retirement.
- An invented worker. The starting balance of zero, the 30-year retirement and the $40,000 target are made up to show the mechanics.
- No taxes or fees. The returns are before tax and before fees. The lesson on fees, taxes and net returns shows how much they take.
- No Social Security or pension. The calculator shows the income from savings alone. The average benefit is quoted for scale and is not added.
- A fixed 30-year horizon. People live for different lengths of time, and the calculator pays out evenly over 30 years rather than testing other lengths.
- Averages from a survey. The Federal Reserve figures describe all US families, and the Social Security average is for retired workers as a group. Neither describes the worker in the calculator.
- No advice. The lesson does not say how much anyone should save, where to invest, or when to retire.
Common mistakes
Ignoring inflation
A large future balance can buy far less than it seems to. Convert it to today’s dollars before judging it.
Using the nominal return as the growth in buying power
Buying power grows at the real return, which is lower than the nominal return when prices are rising.
Thinking a late start only costs the missed contributions
The missed years also lose the growth those contributions would have earned. In the third experiment, a 29% fall in contributions led to a 39% fall in the pot.
Counting on an average return every year
The calculator uses a steady return to show the mechanics. Real returns are uneven, which is a reason to test different returns, not to trust one.
Reading a median as what everyone has
The median balance is the middle holder. Half of the families that held an account had less, and many families had none.
Try it yourself
1. A nominal return of 6% and inflation of 3% give what real return?
Show the working
1.06 ÷ 1.03 = 1.02913, so the real return is 2.91%.
2. A person saves $500 a month for 35 years. How much do they put in, in today’s dollars?
Show the working
500 × 12 × 35 = $210,000.
3. The pot is $356,691 in today’s dollars and $1,003,678 in the money of the day. Which figure shows what it can buy, and why?
Show the working
The first. The second is inflated by 35 years of 3% price rises, 1.0335, about 2.81 times, so it is the same buying power counted in larger numbers.
4. Starting ten years later cuts the contributions by 29%. By what share does the pot fall in the model?
Show the working
The pot falls from $356,691 to $216,263, a fall of 39%, because the lost years had the longest to grow.
5. The average retired-worker benefit in June 2026 was $2,084.40 a month. What is that for a year, and what share of a $40,000 target?
Show the working
2,084.40 × 12 = $25,013, and that divided by 40,000 is 62.5%.
Where this is used
- A worker uses a retirement calculator to see what a monthly contribution could become.
- A planner compares a target income with the income a pot can support.
- An employer’s pension fund projects future liabilities using assumptions about returns and inflation.
- An analyst converts nominal figures into real terms to compare across decades.
- A policymaker reads surveys such as the Survey of Consumer Finances to see how many households hold retirement accounts.
Key terms
- Compounding
- Earning returns on earlier returns.
- Nominal return
- The return before taking inflation into account.
- Real return
- The return after inflation, which is the growth in buying power.
- Today’s dollars
- Amounts adjusted for inflation so that they can be compared.
- Retirement account
- An account that holds savings for retirement, such as an IRA or a workplace plan.
- Defined contribution plan
- A plan in which the balance depends on what is paid in and how it grows.
- Annuity payment
- A level payment made over a fixed number of periods.
- Social Security benefit
- A monthly payment from the US government to eligible retired workers.
- Median
- The middle value, with half above and half below.
Questions people ask
Why does starting early matter so much?
Because early contributions have the most time to compound. In the model, losing ten years cut the pot by far more than it cut the contributions.
Why show the pot in today’s dollars?
Because it tells you what the money can buy. The same pot in future money looks larger only because prices will have risen.
Is $40,000 the right target?
It is an invented figure for comparison. The right target depends on a person’s costs and circumstances.
Does the calculator include Social Security?
No. It shows what the savings alone can pay, and the lesson quotes the average benefit separately.
Sources and review
- Board of Governors of the Federal Reserve System, Changes in U.S. Family Finances from 2022 to 2025: Evidence from the Survey of Consumer Finances (9 October 2026), Table 3 and Box 2, for the share of families holding retirement accounts, the median balance among holders and the mean balances by age among families with an IRA or defined contribution plan, in 2025 dollars.
- US Social Security Administration, Monthly Statistical Snapshot, June 2026, Table 2, for the number of retired-worker beneficiaries and their average monthly benefit.
How the numbers were checked: the balances, the real return, the yearly income and the four experiments were recomputed in plain code from the formulas shown, and the changes in the survey table and the annual benefit were recalculated from the source figures. The calculator, which runs separately, was compared with that code for every combination of settings it allows. The worker is invented.