The honest answer: somewhere between 7% and 10% annually over the long run — but only if you stay invested long enough for that average to actually show up. The number you plug into a calculator is a planning assumption, not a promise, and understanding the difference between the two is what separates investors who stick with it from those who bail at the wrong moment.
The Historical Average Is Real, But It's Not Linear
The S&P 500 has returned roughly 10% per year on average since 1957, or about 7% after adjusting for inflation. That number is real and well-documented. What it hides is the path to get there.
In any given year, the market doesn't return 10%. It returns +26% or -38% or +28% or -19%. The average only emerges across decades. This matters because most people don't experience the average — they experience the sequence. Someone who invested a lump sum in late 2007 sat underwater for four years before getting back to even. Someone who started monthly contributions in 2009 rode one of the longest bull runs in history. Same average, completely different experiences depending on when the clock started.
| Time period | S&P 500 approximate return |
|---|---|
| 1985–2000 | ~18% annualized (exceptional) |
| 2000–2010 | ~-1% annualized (lost decade) |
| 2010–2020 | ~14% annualized (strong bull run) |
| 1985–present | ~10–11% annualized (long-term average) |
The takeaway: the longer your time horizon, the more the actual average has a chance to show up. Over 10-year windows, the S&P 500 has been positive the vast majority of the time in recorded history. Over 20-year windows, it has never delivered a negative return.
What to Use as Your Planning Rate
If you're running numbers in a stock investment calculator, use these as your assumptions:
- Conservative: 6–7% (accounts for inflation, assumes some bonds or diversification)
- Moderate: 8–9% (all-stock, long horizon, historically grounded)
- Optimistic: 10–11% (matches the raw S&P 500 historical average, pre-inflation)
Don't use 12% or higher for serious planning. It's not impossible, but building your retirement around it is risky. Don't use 4–5% if you're 100% in equities with a 30-year horizon either — you're likely underselling what a diversified portfolio can do.
The most useful thing you can do is run your scenario at multiple rates. See what 7% looks like versus 10%. That gap over 30 years is often the difference between "comfortable" and "more than I expected." The uncertainty is the point — planning for a range is smarter than planning for a single number.
Why Monthly Contributions Change Everything
A lump sum invested in the wrong year can take years to recover. Monthly contributions smooth that out. When prices drop, your regular contribution buys more shares. When prices recover, those cheaper shares appreciate. This is dollar-cost averaging and it's one of the few free advantages individual investors actually have.
Run the same investment amount in our stock investment calculator as a lump sum versus spread over 12 months — the difference in final value is often smaller than you'd expect, and the emotional experience of contributing monthly through a downturn is far easier to sustain.
The return you actually earn isn't just a function of what the market does. It's a function of whether you stay invested when it gets uncomfortable. A 7% return that you stick with beats a 10% plan that you abandon at the first crash.