Why volatility contracts and expands
Quiet periods tend to be followed by big moves, and big moves by quiet periods. A Bollinger Band squeeze (the bands at their narrowest in months) flags stocks that have gone quiet; traders then watch for a breakout from the range.
- BB width %: the distance between the upper and lower Bollinger Bands (20 days, 2 standard deviations) as a share of the 20-day average.
- Width rank: where today’s width sits among the last 126 days. 0 is the narrowest, 100 the widest.
- ATR %: the 14-day average true range as a share of the price.
- ADR %: the average high-to-low range over the last 20 days.
Frequently asked questions
Does a squeeze tell me which way it will break?
No. It only says volatility is low. Many traders combine it with the trend (for example, price above the 50-day average) and wait for the breakout itself.
Why do I need an Alpaca key?
US stock prices are licensed data, so they can’t be handed out for free by a website. Alpaca gives anyone a free market-data key that allows 200 requests a minute and returns many stocks per request, which is enough to scan the whole list. Your key is saved only in your browser and is sent only to Alpaca. See how to get a free Alpaca key.
Which stocks does it scan?
About 600 US stocks and ETFs: roughly the S&P 500, popular growth and momentum names, and around 75 of the most traded ETFs. The largest 135 load first; the rest follow automatically a few seconds later.
Is the data real-time?
Alpaca’s free data is 15 minutes behind the market. Daily figures update through the trading day, and the latest candle is the current (unfinished) day while the market is open.