Relative Strength Index RSI Calculator for Prices

The relative strength index (RSI) is a momentum oscillator that scales recent average gains against recent average losses. Readings near 70 or above are commonly treated as potentially overbought; readings near 30 or below as potentially oversold. RSI is not a buy or sell order by itself. It describes how one-sided the last N closing changes have been, which traders then combine with trend, volume, and risk limits. This RSI calculator uses a simple (non-smoothed) average of the last period close-to-close changes. Average gain is the sum of positive changes over those N steps divided by N; average loss is the sum of absolute negative changes divided by N. RSI = 100 − 100 / (1 + average gain / average loss). If there were no losses, RSI is 100; if there were no gains, RSI is 0. You need at least period + 1 prices. A 14-period reading therefore needs 15 closes. Separate prices with commas, spaces, or new lines. Wilder’s original RSI seeds the first average with N changes and then smooths: new average = (prior average × (N − 1) + current change) / N. Platform values that use Wilder smoothing will not match this simple window exactly, especially after long histories. The simple window is easier to audit by hand and still shows when the latest N changes are dominated by gains or losses. Use RSI on the same interval as your prices: daily closes with a 14-day period, hourly closes with a 14-hour period. Do not mix adjusted and unadjusted prints in one list. Overbought in a strong uptrend can persist; oversold in a decline can persist. Treat 70/30 as a conventional label, not a forecast, and do not size a trade from an educational RSI reading alone. If you need to match a broker chart, compare one window by hand before you rely on the number.