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?

How does the TSI differ from the RSI?

What are the best TSI settings?