Your brokerage says your account is “up 8% this year.” Nice. But that number usually doesn’t reflect the messy reality of when you added money — and that timing is exactly what determines your real result.
Here’s how to find your honest, money-weighted return, with numbers you can reproduce on our Investment Return calculator.
The problem with simple returns
A simple “I made X%” treats every dollar as if it were invested for the whole period. But if you added money in March, skipped a month, then added a lump sum in September, those dollars had very different time in the market.
Two investors can hold the same fund, see the same market, and end up with different real returns — purely because of when they contributed. That’s what a money-weighted return captures: it solves for the one constant annual rate that would have turned your actual contribution schedule into your actual final balance.
How the reverse math works
The tool solves the compound formula backwards. Given your starting balance, monthly contribution, years, and final balance, it finds the monthly rate i such that:
FV = P·(1+i)N + M·(((1+i)N − 1)/i)
Then it annualizes that monthly rate. It’s the exact same equation our Compound Interest calculator uses forward — just solved for the rate instead of the balance.
A worked example
Say you started with $10,000, added $500/month for 10 years, and your account is worth $150,000 today.
Total you invested: $70,000 ($10,000 + $500 × 120). Your real annualized return: about 12.2%.
That’s a strong result — comfortably above the long-run stock market average — because the compounding on your early money did most of the work. For scale: the S&P 500 has averaged roughly 10% a year in nominal terms (about 7% after inflation) since 1926, per long-run data from NYU Stern (Source: NYU Stern historical returns) — so a 12.2% money-weighted return over a decade is meaningfully better than the long-run average.
For reference, here’s how different outcomes read at the same contribution schedule ($500/month, 10 years, starting at $0):
| Final balance | What it means | Real return |
|---|---|---|
| $86,542 | Exactly 7% annualized | 7.0% |
| $60,000 | You got your money back, nothing more | 0.0% |
| $50,000 | You lost money after fees/timing | −3.8% |
Notice how a final balance equal to what you put in yields 0% — that’s the honest read. And any result below your total contributions is a negative return, no matter how good the market felt.
Why this matters for judging your investing
A money-weighted return tells you whether your decisions helped or hurt. Compare it to a buy-and-hold benchmark over the same period:
- Your return ≈ benchmark → your timing and contributions neither helped nor hurt.
- Your return > benchmark → you lucked into good timing or favorable contribution timing.
- Your return < benchmark → you added money at bad times, or your fees ate the difference.
That last one is more common than people admit. The tool won’t tell you what to do, but it will tell you the truth about what you’ve actually earned — which is where every improvement starts.
The takeaway
- Know your real number. Simple annual returns lie when your contributions are lumpy — which is everyone.
- Your contributions’ timing is part of your performance. A money-weighted return includes it, honestly.
- Check it against a benchmark. The gap between your real return and the market’s is your true scorecard.
Run your own numbers on the Investment Return calculator — starting balance, monthly additions, years, final value, and it tells you your real annualized return with a full yearly breakdown.