How RSI works
The Relative Strength Index compares the size of recent gains with recent losses on a scale of 0 to 100. Readings under 30 are traditionally called oversold and over 70 overbought. In a strong trend, RSI can stay overbought (or oversold) for weeks, so many traders use it together with a trend filter.
- RSI 14 uses 14 days and Wilder’s smoothing, the same as most charting platforms.
- RSI 2 uses only 2 days. It’s very jumpy and used for short-term mean-reversion: buying sharp dips in stocks above their 200-day average (RSI 2 under 10), or selling rallies in stocks below it (RSI 2 over 90).
Frequently asked questions
Is an oversold stock a buy?
Not by itself. Stocks in a downtrend can stay oversold for a long time. Many traders only take oversold signals in stocks that are still above a long-term average such as the 200-day.
Which markets can it scan?
Four, picked with the Market buttons above the table. Crypto (the default) scans the 250 busiest USDT pairs on Binance. Crypto perps scans the 200 busiest USDT perpetual futures on OKX. Both are free public data and need no key. US stocks scans about 600 US stocks and ETFs with your own free Alpaca key, and CME futures scans about 25 front-month CME Group contracts (stock indexes, Treasuries, oil, gas, metals, grains, livestock, currencies and CME bitcoin) with your own free Massive key.
Why do stocks and futures need a key?
Stock and futures prices are licensed data, so a website can’t hand them out for free. Alpaca (for stocks) and Massive (for futures) give anyone a free data key. Your key is saved only in your browser and sent only to that provider. See how to get a free Alpaca key and how to get a free Massive key for futures.
Which stocks does it scan with an Alpaca key?
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?
Crypto and crypto perps are live from Binance and OKX, on daily candles that start at 00:00 UTC (today’s candle is still forming). Alpaca’s free stock data is 15 minutes behind the market, and Massive’s free futures plan is 8 hours delayed. Turn on auto-refresh next to the results to update the table in place every 30 seconds, minute or 5 minutes.