Historical volatility is a statistical measure of how much an investment's price has moved up and down over a past period, usually expressed as an annualized percentage. It's calculated using the standard deviation of an asset's returns and tells you how much price swings to expect based on recent behavior. For angel investors evaluating startups or public companies, historical volatility provides concrete data about an investment's risk profile.
How It Works
Historical volatility uses past price data—typically from 30 days to several years—to calculate how much returns deviated from their average. A higher volatility percentage means bigger price swings; a lower percentage means more stable pricing. The calculation takes daily, weekly, or monthly returns, finds the standard deviation, and annualizes the result. For example, if a stock traded at $100 with price movements that produced a 30% annualized historical volatility, you'd expect larger price swings than a stock with 10% volatility.
Why It Matters for Investors
Historical volatility helps you understand your portfolio's risk. It's especially relevant for angel investors because early-stage companies and growth stocks typically show higher volatility than established enterprises. Knowing the volatility of your investments lets you make informed decisions about position sizing and portfolio balance. It also helps you compare similar investments—a tech stock with 45% volatility carries more price risk than one with 20% volatility. Understanding this metric helps align your investment choices with your risk tolerance and time horizon.
Example
Imagine comparing two growth companies for investment. Company A has traded with prices swinging 60% annually based on its historical volatility, while Company B shows 25% historical volatility. If both have similar fundamentals, the 60% volatility tells you Company A's stock price will likely experience more dramatic ups and downs. This doesn't make it worse—some investors seek higher volatility for potential returns—but it clarifies the risk you're taking. A portfolio weighted too heavily toward high-volatility positions might experience significant value swings that stress unprepared investors.
Key Takeaways
- Historical volatility is a backward-looking measure of how much an asset's price has fluctuated, calculated using standard deviation of returns
- Higher volatility percentages indicate larger price swings and greater risk; lower volatility suggests more stable pricing
- Use it to compare investment risk profiles and size positions appropriately for your risk tolerance
- Don't confuse it with implied volatility, which predicts future price swings based on options pricing
- Early-stage companies typically have higher historical volatility than mature businesses, a key consideration for angel investing