What this calculator tells you
You’re 30, you’ve got $25,000 saved, and you toss $500 into your 401(k) every month. At a 7% average return, where do you land by 65? Around $1.16 million. The part that surprises most people: you only put in about $235,000 of that. The other $925,000 is growth on top of growth.
That gap is the whole point of saving early. This tool projects your nest egg month by month, compounding your balance and adding each contribution along the way. Then it splits the final number into two buckets so you can see exactly how much is your own money versus how much the market did for you.
How to use it
Five inputs, that’s it. Your current age, the age you want to retire, what you’ve already saved, how much you add each month, and the annual return you expect. The projection updates the moment you change anything.
A few notes on the numbers:
- Current savings is your starting balance across every retirement account combined: 401(k), IRA, brokerage, whatever counts.
- Monthly contribution is what you actually add, not including any employer match (add the match in if you want to see it).
- Expected return trips people up. The S&P 500 has averaged roughly 10% nominally over decades, but after inflation it’s closer to 7%. Using 6 to 7% keeps your projection grounded in real spending power.
Hit Download to pull a year-by-year CSV, or Copy to grab the summary for a spreadsheet or a note to your future self.
Why early beats more
Run two scenarios and the lesson jumps out. Someone who saves $400 a month from 25 to 65 ends up well ahead of someone who saves $600 a month from 35 to 65, even though the second person contributes more total dollars. Time in the market does the heavy lifting.
Try it yourself. Bump your current age up by five years and watch the nest egg shrink by a chunk that feels disproportionate. That’s compounding working against you when you wait. Then bump your monthly contribution by $100 and see how much ground that recovers. These two levers, time and amount, are the ones you actually control.
Good to know
This is a projection, not a promise. Real returns bounce around year to year, and a smooth 7% line never happens in reality. Markets crash, recover, stall, and surge. The tool assumes a steady average because that’s the only honest way to model decades ahead without pretending to predict 2041’s market.
It also doesn’t bake in inflation, taxes, or fees. If you want your result in today’s dollars, plug in a lower return (say, your expected return minus 3% for inflation) and the final figure roughly reflects real buying power. Everything stays in your browser. Nothing about your finances gets sent anywhere.
Common questions
What return rate should I use? For a stock-heavy portfolio, 6 to 7% is a reasonable long-run assumption after inflation. Bond-heavy or conservative mixes run lower, around 3 to 5%.
Does it include my employer match? Not automatically. If your employer matches part of your contribution, add that amount into the monthly contribution field to see the fuller picture.
Why is the growth so much bigger than what I put in? That’s compounding. Early contributions sit in the market the longest, so they multiply the most. The longer your timeline, the more lopsided the growth-to-contributions split gets.
Is this in today’s dollars or future dollars? Future dollars by default. To approximate today’s buying power, subtract about 3% from your expected return before entering it.
Can I model recurring raises to my contribution? Not yet. The monthly amount stays flat across the whole projection. To estimate a step-up, run it again with a higher contribution and compare the two nest eggs.