What Is the Difference Between Historical Volatility and Implied Volatility?
Direct answer
Historical vs implied volatility
Historical volatility, also called realised volatility, is the standard deviation of an asset's daily returns over a past window, multiplied by the square root of 252 to express it as an annual percentage. Implied volatility is the market's forecast of future volatility derived from option prices, such as the VIX for the S&P 500. In our data from 2017 to November 2026, the S&P 500's 30-day realised volatility averaged 15.0% while the VIX averaged 18.7%, and the VIX was above realised volatility about 86% of the time: option buyers usually pay a premium. Realised volatility ranged from 3.5% in October 2017 to 84.4% in April 2020.
- Historical = standard deviation of past daily returns × √252
- Implied = volatility priced into options (VIX for the S&P 500)
- 2017–2026 averages: realised 15.0%, VIX 18.7%
- VIX above realised about 86% of the time (a volatility risk premium)
- Range of S&P 500 30-day realised: 3.5% (Oct 2017) to 84.4% (Apr 2020)
"Volatility" gets used for two different things: how much a market has moved, and how much options traders expect it to move. Mixing them up leads to bad conclusions about risk and about option prices.
What people on X are asking
In April 2025 one user asked a market commentator to show implied versus historical volatility for the Nikkei, S&P 500, Nasdaq, DAX and other indices. In July 2025 an account posted about implied versus realised volatility and why the gap matters for option straddles. In March 2026 a trader compared E-mini S&P implied and 20-day historical volatility, noting implied had been climbing while realised faded. Here is the measure, with our own numbers for the S&P 500.
The fact-checked answer
How historical volatility is calculated. Take daily log returns (the natural log of today's close divided by yesterday's). Compute their standard deviation over a window, for example 30 trading days. Multiply by the square root of 252, the approximate number of trading days in a year, to annualise it. A result of 16% means daily moves have been about 1% on average (16 ÷ √252 ≈ 1.0).
UXS chart
S&P 500: 30-day realised volatility vs the VIX (%)
Realised volatility, 30 days: latest
11.23%
November 4, 2026
VIX (30-day implied): latest
25.64%
November 6, 2026
Year by year: Realised volatility, 30 days
Computed by UXS from the same data as the chart. Tap a column header to sort. * = year to date (latest data November 4, 2026).
| 2026* | 11.23% | +0.21 pts | 17.88% | 8.07% | 25.64% |
| 2025 | 11.02% | -1.37 pts | 41.61% | 6.57% | 14.95% |
| 2024 | 12.39% | +4.28 pts | 19.71% | 6.77% | 17.35% |
| 2023 | 8.11% | -10.51 pts | 19.74% | 7.99% | 12.45% |
| 2022 | 18.62% | +1.26 pts | 31.69% | 15.25% | 21.67% |
| 2021 | 17.36% | +7.59 pts | 18.92% | 7.38% | 17.22% |
| 2020 | 9.77% | +2.81 pts | 84.42% | 6.45% | 22.75% |
| 2019 | 6.96% | -19.30 pts | 28.46% | 5.47% | 13.78% |
| 2018 | 26.26% | +19.97 pts | 26.29% | 5.65% | 25.42% |
| 2017 | 6.29% | – | 8.96% | 3.50% | 11.04% |
What implied volatility is. The VIX, published by Cboe, is calculated from S&P 500 option prices and estimates expected volatility over the next 30 days. It is forward-looking: if traders expect turbulence, they pay more for options and the VIX rises. For the full story see what the VIX is.
Why implied is usually higher. Over 2017–2026, the VIX averaged 18.7% and 30-day realised volatility 15.0%, and the VIX was above realised about 86% of the time. Option sellers demand compensation for the risk of sudden crashes, so implied volatility tends to trade above what is later realised. The gap is called the volatility risk premium. It reverses in shocks: when markets crash, realised volatility jumps faster than implied, as in March–April 2020.
S&P 500: VIX vs realised volatility, yearly averages
Computed by UXS from FRED VIXCLS and SP500. Realised = 30-day window, annualised. Tap a column header to sort.
| 2017 | 11.1 | 6.6 | 4.5 |
| 2020 | 29.3 | 27.1 | 2.2 |
| 2022 | 25.6 | 23.4 | 2.2 |
| 2024 | 15.6 | 11.9 | 3.7 |
| 2026 (to Nov) | 18.2 | 12.4 | 5.8 |
| 2017–2026 | 18.7 | 15.0 | 3.7 |
The range. The S&P 500's 30-day realised volatility fell to 3.5% in October 2017, one of the calmest stretches in modern markets, and peaked at 84.4% in early April 2020, when the window covered the March crash. In early November 2026 it was 16.9% while the VIX was 28.18, a wide gap that showed traders paying up for protection after a sharp pullback.
How traders use the two.
- Position sizing: realised volatility tells you how far a market actually moves, which helps size positions and set stops. See how much to risk per trade.
- Option pricing: comparing implied with realised volatility shows whether options look expensive or cheap. Buying options when implied is far above realised means paying a big premium.
- Regime changes: a jump in realised volatility often comes with falling prices; see how volatile Bitcoin is compared with stocks and gold for the same measure on other assets.
Limitations. Historical volatility depends on the window: 10 days reacts fast, 90 days is smooth. It assumes moves are spread evenly, so it understates the risk of single-day crashes. And past volatility is not a forecast.
Commodity implied-volatility indices work the same way; see what an OVX spike means for oil traders.
Implied volatility sets the premium you risk; see how much you can lose buying an option.
Decision helper
| Situation | What it suggests |
|---|---|
| Implied far above realised | Options expensive; fear priced in |
| Implied below realised | Options cheap relative to recent moves (rare) |
| Realised rising fast | Risk rising; reduce size |
| Both low | Calm, but calm can end abruptly |
Common mistakes
- Comparing implied and realised volatility over different windows.
- Forgetting to annualise, or annualising with the wrong day count.
- Treating low volatility as low risk.
- Assuming implied volatility predicts direction.
FAQ
What is historical volatility?
The annualised standard deviation of past daily returns.
How is it different from implied volatility?
Implied volatility is derived from option prices and looks forward; historical looks back.
Is the VIX historical or implied?
Implied: it is calculated from S&P 500 option prices.
Why is implied volatility usually higher?
Option sellers demand a premium for crash risk.
What is a normal volatility for the S&P 500?
Its 30-day realised volatility averaged about 15% from 2017 to 2026.
What window should I use?
20–30 days is common; shorter is more reactive and noisier.
Sources
- Cboe: VIX index
- FRED: CBOE Volatility Index (VIXCLS)
- FRED: S&P 500 (SP500)
- Investor.gov: Diversify your investments
Facts checked November 10, 2026. X posts are cited as evidence of the question, not of the answer.