True Strength Index explained

Momentum

What True Strength Index measures

TSI double-smooths the day-to-day price change with two successive EMAs (default 25 then 13 periods), and does the same to the absolute price change, then expresses the ratio as a percentage. The double smoothing gives a momentum reading that's both responsive to genuine trend shifts and meaningfully quieter than a single-smoothed oscillator like RSI.

How True Strength Index readings are interpreted

TSI oscillates roughly between -100 and +100, though in practice most price action keeps it within a tighter -50/+50 band. Positive TSI means net upward momentum over the smoothed lookback; negative means net downward momentum. A signal-line cross (TSI vs. its own short EMA) is the typical entry/exit trigger.

Conventional True Strength Index levels

TSI crosses above its signal line: conventionally read as bullish
TSI crosses below its signal line: conventionally read as bearish
TSI crosses above zero: broader confirmation of an uptrend developing
Extreme readings (roughly beyond ±25) are historically associated with overbought/oversold conditions, though the exact level varies by security
Divergence between TSI and price is treated the same way as RSI divergence — a warning of weakening momentum

Where True Strength Index works, and where it does not

The double smoothing makes TSI considerably less noisy than RSI or Stochastic, at the cost of being somewhat slower to react. Works across most timeframes; more commonly used on daily charts for swing trading than for very short-term signals.

Indicators commonly read alongside True Strength Index

MACD: Both are trend-following momentum tools with a signal-line cross mechanic — agreement adds confidence
RSI: TSI divergence confirming an RSI divergence is a stronger combined signal
ADX: TSI signal-line crosses are more reliable when ADX confirms an actual trend is underway

Known limitations of True Strength Index

The double smoothing means TSI is meaningfully slower than RSI at signaling a fresh reversal
Unlike RSI, there's no universally agreed overbought/oversold threshold — it varies by security and needs some calibration
In choppy markets the signal-line cross can still whipsaw, just less often than faster oscillators

True Strength Index in practice

The signal-line cross is conventionally treated as the primary signal rather than raw zero-crosses alone
Because it's smoother than RSI, TSI divergence signals are generally considered more reliable — worth prioritizing over RSI divergence when the two disagree
Works well as a secondary confirmation tool alongside a faster primary indicator rather than as the sole signal
Best suited to swing trading given its smoothing lag — not ideal for very short holding periods

Other momentum indicators

Chande Momentum Oscillator
Know Sure Thing
Percentage Price Oscillator
TTM Squeeze

Testing ideas built on True Strength Index

A reading of True Strength Index can be written as an exact rule and checked against historical data — as a full strategy with entries, exits and costs, or as a single condition and what followed it:

How to backtest a trading strategy without code
Event analysis: what follows a market event

Plot it yourself. Add this indicator to a chart, change every parameter and watch the line move, then backtest how the rule would have behaved on historical data — free on the S&P 500 ETF, no card.

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This is reference material, not advice. It describes what each indicator measures and how its readings are conventionally interpreted. Nothing here is a recommendation to buy or sell anything, and no indicator predicts future prices. GU Analyser is an analytical tool — no money is ever traded here.