RSI Calculator

The Relative Strength Index, developed by J. Welles Wilder and introduced in 1978, is a momentum oscillator that measures the speed and size of recent price changes on a bounded scale from 0 to 100. It is designed to answer a single question: over the lookback window, how much of the total movement has been to the upside versus the downside?

The calculation begins by separating each bar's change from the previous close into a gain (upward moves) or a loss (downward moves, taken as a positive number). Wilder's smoothed average of the gains and of the losses over the period gives the relative strength, RS = average gain / average loss. RSI is then RSI = 100 − 100 / (1 + RS). When there are no losses in the window, RSI is defined as 100. The default lookback is 14 periods, the value Wilder originally proposed.

RSI is one of the most widely watched momentum tools because it compresses a messy price history into a single, easy-to-read number. Readings are traditionally described as overbought above 70 and oversold below 30, though these are long-standing conventions rather than rules, and many analysts shift them in strongly trending markets where an instrument can stay overbought or oversold for a long time.

Beyond the raw level, a common area of study is RSI divergence, where price makes a new high or low that the oscillator does not confirm, and the midline near 50, which some treat as a rough gauge of whether momentum leans up or down. What any of these observations mean, and whether they matter to you, is entirely a matter of your own analysis.

TradingView is one of the most widely used charting and market-analysis platforms, where traders and analysts study price movement across stocks, crypto, forex, and futures on interactive charts. Pine Script is TradingView's own lightweight programming language, created so anyone can build custom tools that run directly on those charts.

People use Pine Script to build four main kinds of tools. Indicators calculate and plot values on the chart, exactly like the calculation above, but recomputed automatically on every bar. Strategies add explicit entry and exit rules and can be backtested against historical data in TradingView's Strategy Tester to see how they would have behaved. Screeners scan many symbols at once for conditions you define. Alerts notify you the moment a condition you specified occurs, so you do not have to watch the screen.

The value is precision and automation. Instead of eyeballing a chart, you describe exactly what you want measured, visualized, or notified about, and TradingView runs it consistently across any market and timeframe. That is why traders, analysts, and developers write Pine Script: it turns a manual charting idea into a repeatable tool. These tools are for tracking, visualizing, and testing market ideas; they do not tell you what to trade, and that decision always remains yours.

Writing that code by hand means learning Pine Script's syntax, its type system, and the exact names of hundreds of built-in functions. It is a real programming language, and small mistakes stop a script from compiling in the Pine Editor.