Retirement calculator

Reembun. (2026, July 28). Retirement calculator. https://reembun.com/retirement-calculator

The projection

Compound growth with regular contributions:

A = P(1 + r/n)^(nt) + PMT × [ ((1 + r/n)^(nt) − 1) / (r/n) ]

where P is what you have saved, PMT the monthly contribution, r the annual return, n the compounding periods and t the years remaining.

Real returns, done properly

Showing a projection in future nominal money is close to useless. $2 million in 2060 means nothing without knowing what it buys. So the calculator works in today’s purchasing power using an inflation-adjusted return.

The correct relationship is Fisher’s, which divides rather than subtracts:

real rate = (1 + nominal) / (1 + inflation) − 1

At 7% nominal and 3% inflation that gives 3.88%, not 4%. The 0.12 percentage point difference is trivial in one year and worth several per cent of the final pot over thirty.

A worked example

Age 30, retiring at 65, $25,000 saved, $500 a month, 7% nominal return, 3% inflation:

	Nominal	Today’s money
Pot at 65	$1,143,000	$407,000
You contributed	$235,000	$235,000
Growth	$908,000	$172,000

The nominal figure looks transformative and the real figure looks merely solid. The real figure is the one that tells you what your retirement will actually feel like, and the gap between them is why inflation deserves more attention than return assumptions usually get.

Time in the market

The single most consequential variable is how long the money compounds, not how much you put in.

Start at	Monthly	Total paid in	Real pot at 65
25	$400	$192,000	$379,000
35	$600	$216,000	$310,000
45	$1,000	$240,000	$216,000

Each saver pays in a similar amount. The one who started at 25 finishes with three quarters more than the one who started at 45, purely from twenty extra years of compounding.

Turning a pot into an income

The 4% rule comes from the Trinity study, which tested historical US withdrawal rates over 30-year retirements. It suggests withdrawing 4% in year one, then adjusting that amount for inflation each year.

Withdrawal rate	Income from $500,000
3%	$15,000 a year
3.5%	$17,500 a year
4%	$20,000 a year
5%	$25,000 a year

It is a heuristic derived from one country’s market history at one particular asset allocation. Longer retirements, different markets, higher fees and lower expected returns all argue for something below 4%.

What no calculator can model

Sequence-of-returns risk. A portfolio that falls 30% in your first two years of retirement and then recovers is worth far less to you than one that rises first and falls later, even at an identical average return. Withdrawals during a drawdown sell more units to raise the same cash.

Fees. A 1% annual platform and fund fee on the example above costs roughly $80,000 of the real final pot. Fees compound against you exactly as returns compound for you.

Tax. Contributions, growth and withdrawals are all taxed differently depending on the account type and the country, and the rules change over the decades this projection spans.

Use this to understand the shape of the problem: how much difference an extra decade or an extra hundred a month makes. For decisions, talk to a regulated financial adviser who can see your whole position.