What a retirement pot reaches in twenty-five years
Retirement saving is the clearest case of compounding, because the horizon is long enough for growth to outweigh contributions. This calculator shows where that crossover happens on your numbers.
The figure it produces is a balance at retirement, not an income. Turning one into the other is a separate calculation with its own assumptions about how long the money must last.
The formula behind the number
Two things grow at once: the sum already invested, and each new contribution from the moment it arrives. Together they give:
Here P is the opening balance, M the monthly contribution, i the monthly return and n the number of months. The second term is why contributions made early matter more than contributions made late: each one is multiplied by growth for every month it remains invested.
Worked example: $50,000 plus $1,000 a month for 25 years
The calculator opens on a starting balance of $50,000 plus $1,000 every month, at 6% a year for 25 years.
- Total paid in: $350,000
- Ending balance: $916,242
- Growth: $566,242, which is 162% of what you contributed
Growth exceeds contributions well before the end. That is the whole argument for starting early rather than saving harder later.
Why the second half does the heavy lifting
At the halfway point, after 12 years, the balance is $328,262 — around 36% of the final figure, not half of it.
| Year | Paid in | Growth | Balance |
|---|---|---|---|
| 5 | $110,000 | $27,213 | $137,213 |
| 10 | $170,000 | $84,849 | $254,849 |
| 15 | $230,000 | $183,523 | $413,523 |
| 20 | $290,000 | $337,551 | $627,551 |
| 25 | $350,000 | $566,242 | $916,242 |
The balance roughly doubles in the final third of the term without any increase in what you pay in. Nothing changes except the size of the base being compounded.
What starting late costs
Delay by 5 years and, contributing at the same rate, you end with $627,551 instead of $916,242. That is $288,691 less for $60,000 of skipped contributions — the gap is the growth those early payments would have earned.
How sensitive is this to the return
The rate is an assumption, not a fact, so it is worth seeing the range. Two points higher gives $1,318,035; two points lower gives $649,818. This is why a fee of one percent a year matters so much over decades: it comes straight off the return in this table.
What this calculator leaves out
Inflation, tax on gains, platform and fund fees, and any employer contribution. A 6% nominal return with 2% inflation is closer to 4% in purchasing power, which changes the ending figure substantially.
Turning the pot into an income
A balance is not a pension. The common rule of thumb withdraws 4% of the pot in the first year and adjusts that amount for inflation afterwards, which on $916,000 is about $36,600 a year, or $3,050 a month before tax.
Whether that is enough depends on what you spend, not on what you saved. Work backwards from your expected outgoings and the required pot usually looks different from the one you had in mind.
Related calculators
- Withdrawal calculator — turns the balance into a monthly income
- Financial independence calculator — the target multiple of annual spending
- Inflation calculator — what the ending figure is worth in today’s money