RSI Explained: The Relative Strength Index

The RSI indicator (Relative Strength Index) is a momentum oscillator that measures how strongly an asset's price has risen compared with how strongly it has fallen over a recent period, shown on a scale from 0 to 100. Readings above 70 are traditionally called "overbought" and below 30 "oversold," but in trending markets these levels describe strong momentum rather than guaranteed reversals.

RSI was introduced by J. Welles Wilder Jr. in his 1978 book New Concepts in Technical Trading Systems, and it is now built into virtually every charting tool. It is popular in crypto because it is simple and works on any time frame. It is also widely misused. This guide explains how RSI is calculated, how to read it, and the mistakes that lead traders astray.

How the RSI Is Calculated

You do not need to calculate RSI by hand, but understanding the formula helps you interpret it:

1. 1For each period, record the gain (if the close was higher than the previous close) or the loss (if lower).
2. 2Calculate the average gain and average loss over the chosen number of periods, typically 14. Wilder used a smoothing method that gives weight to past averages.
3. 3Divide average gain by average loss to get relative strength (RS).
4. 4Convert it to a 0–100 scale: RSI = 100 − 100 ÷ (1 + RS).

If gains dominate, RSI moves toward 100. If losses dominate, it moves toward 0. When gains and losses are roughly equal, RSI sits near 50.

How to Read the RSI

The centerline

Many traders watch the 50 level. RSI holding above 50 suggests buyers have been in control on average; below 50 suggests sellers. This is often more useful than the 70/30 extremes.

Adjusting thresholds

Some traders use 80/20 instead of 70/30 to reduce false signals in volatile assets. In a long uptrend, RSI may oscillate between roughly 40 and 80; in a downtrend, between roughly 20 and 60. These ranges are rules of thumb, not laws. See also: Bull Trap vs Real Breakout.

RSI Divergence

A divergence occurs when price and RSI disagree:

• Bearish divergence: price makes a higher high, but RSI makes a lower high. Upward momentum may be fading.
• Bullish divergence: price makes a lower low, but RSI makes a higher low. Downward momentum may be fading.

Divergences are best treated as warnings. In strong trends, several divergences can appear in a row while price keeps moving in the same direction. Related reading: Candlestick Patterns Every Beginner Should Know.

How Traders Use RSI in Practice

Common approaches include:

1. 1Trend confirmation. Use a trend tool such as moving averages to define the trend, then use RSI to judge momentum within it.
2. 2Pullback entries. In an uptrend, some traders watch for RSI to dip toward 40–50 and turn up again.
3. 3Multiple time frames. Check RSI on a higher time frame, such as daily, before acting on a lower one, such as hourly.
4. 4Combining with levels. RSI readings near support and resistance areas may carry more weight than readings in the middle of a range.

No approach works all the time. RSI is a description of recent price behavior, and it cannot account for news, liquidations or sudden shifts in sentiment. We cover this in more detail in MACD Explained.

Common RSI Mistakes

• Selling just because RSI is above 70. In strong rallies, this can mean exiting very early.
• Buying just because RSI is below 30. Assets in a downtrend can stay oversold while losing much more value.
• Using very short time frames. One-minute or five-minute RSI produces many signals, most of them noise.
• Ignoring liquidity. On thinly traded tokens, a few trades can swing RSI sharply. Check volume first; our guide to volume analysis explains why.
• Treating backtests as guarantees. A setting that worked in the past may not work in a different market.
• Forgetting risk management. Any indicator-based strategy needs position sizing and an exit plan.

RSI in Crypto Specifically

Crypto trades around the clock, so a "daily" candle depends on the time zone your chart uses, and RSI values can differ slightly between platforms. Crypto assets can also trend harder and reverse faster than many traditional markets. Large assets such as Bitcoin tend to give cleaner readings than small, illiquid tokens. You can view broader sentiment alongside price using the Fear & Greed index.

Bottom line

RSI is a simple, useful way to see whether recent momentum has been strong or weak. Read 70 and 30 as signs of strong momentum, not automatic turning points, pay attention to the 50 line and to divergences, and always combine RSI with trend, volume and a clear risk plan. Used that way, it is a helpful tool; used alone, it is an easy way to lose money. For more on chart tools, see our guide to reading a crypto price chart.