# True Strength Index True Strength Index is an indicator on [Vela](https://vela.luxalgo.com/chart), our next-generation charting platform, written in Pine Script®. The True Strength Index double-smooths one-bar price change and its absolute value with successive EMAs, then plots their ratio as a momentum oscillator centered on zero. It uses the classic defaults of 25 and 13 for the two smoothing lengths with a 13-period signal line. The build reproduces the standard published calculation without modification. - Indicator in the LuxAlgo Library, by LuxAlgo, published Apr 13, 2020. - Access: free. - Concepts: [True Strength Index](https://www.luxalgo.com/library/concept/true-strength-index/) (primary) - Open on Vela: https://vela.luxalgo.com/chart?pineScriptCodeId=nojzkmp2fm5r9r03wqdqazua - Page: https://www.luxalgo.com/library/indicator/true-strength-index/ The **True Strength Index (TSI)** double-smooths one-bar price change and its absolute value with successive EMAs, then plots their ratio as a momentum oscillator centered on zero. William Blau's ratio asks how much of recent movement has been directional: the numerator keeps each bar's sign, the denominator strips it, bounding the line between +100 and -100 by design. This build reproduces the standard published calculation without modification, using the classic 25 and 13 smoothing lengths with a 13-period EMA signal line and a dashed zero line. ## How to Trade the True Strength Index? - **TSI above zero**: smoothed up momentum outweighs down momentum, the regime read favoring longs. - **TSI below zero**: sustained stretches below zero define the bearish regime. - **TSI crossing above the Signal line**: the timing trigger, earlier and less reliable than zero crosses; many honor only crosses agreeing with the zero-line side. - **TSI crossing below the Signal line**: the mirror trigger, filtered the same way. - **Divergence at extremes**: the deep smoothing yields clean swings, so higher-low and lower-high comparisons against price are easy to mark. The same smoothing sets the cost: the line turns after price, and in ranges small oscillations around zero flip the sign without saying much. ## True Strength Index Settings - **Long Length** (default 25): the first (long) EMA applied to the one-bar price change; it does the heavy filtering. Raising it steadies the line and deepens the lag. - **Short Length** (default 13): the second (short) EMA applied to the long-smoothed change, shaping response within the filter. - **Signal Length** (default 13): the EMA of TSI forming the signal line; shorter trades cross quality for speed. ## Alerts Four alert conditions: TSI crossing above or below its signal line, and above or below the zero line. ## Frequently Asked Questions ### Why is the TSI bounded between +100 and -100? The denominator, double-smoothed absolute price change, can never be smaller in magnitude than the double-smoothed signed change above it, so the ratio stays within plus and minus one before scaling by 100. Readings near the limits rarely print. ### How does the TSI differ from the RSI? RSI works from average gains and losses over a single Wilder-smoothed window on a 0 to 100 scale; the TSI double-smooths signed momentum on a zero-centered scale. Its sign carries regime information RSI's 50 line only approximates, and its trace is smoother, the price being later turns. ### What are the best TSI settings? The 25/13 smoothing with a 13-period signal is the published standard. Shorter suits swing timing, longer position bias; the pairing matters most: Long Length sets the filter, Short Length the response within it. ## Related indicators - [Internal Candle Strength](https://www.luxalgo.com/library/indicator/internal-candle-strength/) (Balance of Power): markdown at https://www.luxalgo.com/library/indicator/internal-candle-strength.md - [Pretty Good Oscillator](https://www.luxalgo.com/library/indicator/pretty-good-oscillator/) (Momentum & Oscillators): markdown at https://www.luxalgo.com/library/indicator/pretty-good-oscillator.md - [Gator Oscillator](https://www.luxalgo.com/library/indicator/gator-oscillator/) (Momentum & Oscillators): markdown at https://www.luxalgo.com/library/indicator/gator-oscillator.md - [Wave Trend Oscillator](https://www.luxalgo.com/library/indicator/wave-trend-oscillator/) (Momentum & Oscillators): markdown at https://www.luxalgo.com/library/indicator/wave-trend-oscillator.md - [Traders Dynamic Index](https://www.luxalgo.com/library/indicator/traders-dynamic-index/) (Momentum & Oscillators): markdown at https://www.luxalgo.com/library/indicator/traders-dynamic-index.md - [Center of Gravity](https://www.luxalgo.com/library/indicator/center-of-gravity/) (Momentum & Oscillators): markdown at https://www.luxalgo.com/library/indicator/center-of-gravity.md - [QQE Weighted Oscillator](https://www.luxalgo.com/library/indicator/qqe-weighted-oscillator/) (QQE): markdown at https://www.luxalgo.com/library/indicator/qqe-weighted-oscillator.md - [5/35 Oscillator](https://www.luxalgo.com/library/indicator/5-35-oscillator/) (Momentum & Oscillators): markdown at https://www.luxalgo.com/library/indicator/5-35-oscillator.md --- Source: https://www.luxalgo.com/library/indicator/true-strength-index/ (LuxAlgo Library). Free to use with attribution: https://www.luxalgo.com/library/license/