How the sums work
I start from your current savings and run the balance forward a month at a time: apply a month's growth at the annual rate divided by 12, add your contribution, repeat until the balance crosses $1,000,000. The age at the milestone is just your current age plus the months elapsed. Contributions by then are your starting balance plus every monthly payment; growth's share is roughly the rest of the million.
The chart makes the shape obvious. It's slow and nearly straight for years while contributions do the heavy lifting, then it steepens as the balance itself starts earning serious money. The last few hundred thousand arrive far faster than the first.
Worked example
With the defaults, starting with $20,000 and adding $500 a month at 7%, the first million arrives after 401 months, 33 years and 5 months, at age 63.4 for a 30 year old.
Frequently asked questions
Is $1,000,000 still a meaningful target?
Less than it used to be, and less every year, because inflation quietly erodes what a million buys. It's still a decent round-number milestone and a real psychological marker, just don't treat it as a retirement plan on its own. The inflation calculator shows what it'll be worth by the time you arrive.
What helps most: contributions or returns?
It changes over time. Early on, contributions do almost all the work because there's little balance for returns to act on. Later, the return on a large balance dwarfs anything you add. Time helps at every stage, which is why starting early beats starting big.
Why does this compound monthly?
Because that's how most people invest: a contribution each month, with each one starting to grow as soon as it lands. Monthly compounding at the annual rate divided by 12 is the standard convention for that pattern, and it keeps the result honest for regular savers.