Compound Interest Calculator
What a monthly amount grows to, how much of it is growth rather than your own money, and what waiting to start would cost.
Your money
What it earns
7% is the long-run stock market return after inflation.
Fund and platform fees, taken off the return. A 1% fee removes about a quarter of the result over 30 years.
How long
Your money over time
$750 a month grows to $914,978 in 30 years. You put in $270,000; the rest is growth.
Value over 30 years
The grey line is only the money you put in.
The cost of waiting
Same $750 a month, same end date, started later.
How it's calculated
Each month the balance grows by a twelfth of the yearly return and then the monthly amount is added. Growth earns growth: the money added in the first years does most of the work, because it compounds the longest.
Fees come straight off the return, every year, on the whole balance. A 1% fee on a 7% return leaves 6%, which sounds small and costs roughly a quarter of the final value over thirty years.
The cost of waiting keeps the same monthly amount and the same end date but starts later, so it puts in less and, more importantly, misses the earliest years. That is why starting ten years earlier can beat contributing for thirty.