📶
Bollinger Bands Calculator
Live upper and lower volatility bands, computed from real daily closing prices.
Computed from real daily closing prices (20-day SMA, ±2 std dev) over the last ~2 months. Data via Yahoo Finance.
Bollinger Bands place an upper and lower band around a 20-day simple moving average, each offset by two standard deviations of real recent closing prices for the ticker you enter.
Bands widen during high volatility and narrow during low volatility ('squeezes'), which traders often watch as a precursor to a potential breakout in either direction.
FAQ
What do Bollinger Bands show?
They plot bands a set number of standard deviations above and below a moving average, expanding and contracting with volatility — price near the outer bands is statistically stretched relative to its recent range.
Why is 2 the default multiplier?
Two standard deviations captures roughly 95% of price action under a normal distribution assumption, making it a common default, though it can be adjusted for different volatility regimes.