TSI indicator: a guide to the True Strength Index

The true strength index (TSI) is a double-smoothed momentum oscillator. It can help traders assess whether recent price moves have been driven more by upward or downward momentum.

Below, we’ll look at how the TSI is calculated, how traders may read its main signals and what to keep in mind before using it as part of a broader analysis.

What is the TSI indicator?

The true strength index (TSI) is a momentum oscillator that looks at both the direction and the strength of price movement. It was developed by William Blau and introduced in Stocks & Commodities magazine in 1991. Instead of reacting directly to each price change, the TSI smooths that change twice using exponential moving averages, which is why it is often described as a ‘double-smoothed’ momentum tool (Traders.com, 1991).

The result is a line that moves above and below a central zero level, broadly from roughly -100 to +100. Positive values suggest that upward momentum has been stronger, while negative values suggest that downward momentum has been stronger. Because the indicator smooths price change twice, it can filter out some short-term noise and produce a cleaner line than many single-smoothed oscillators.

That smoothness can make the TSI easier to read, especially for traders who want to focus on the wider momentum picture rather than every small move. However, smoothing also means the indicator may respond later than price itself.

How is the TSI calculated?

The TSI compares double-smoothed price change with double-smoothed absolute price change, then expresses the result as a percentage.

Past performance is not a reliable indicator of future results.

Many traders also plot a signal line, which is an EMA of the TSI itself, commonly set to 7 or 13 periods. The signal line moves more slowly than the TSI and is used as a reference for crossovers, in a similar way to the signal line on the MACD.

Past performance is not a reliable indicator of future results.

How the TSI works in trading

Because the TSI moves above and below zero, the centre line is often an important reference point. A move from negative to positive territory may suggest that upward momentum has started to outweigh downward momentum. A move from positive to negative territory may suggest the opposite.

Traders who use this approach often treat the zero line as a broad momentum guide rather than a precise trading signal.

Common TSI signals

The TSI can also reach stretched readings. Levels around +25 are sometimes described as an overbought zone, and levels around -25 as an oversold zone, though these levels are not fixed.

They can vary depending on the instrument, timeframe and smoothing settings. A level that looks stretched on a calmer currency pair such as EUR/USD may be less notable on a more volatile asset. For that reason, traders often adjust these zones to the market they are studying rather than applying the same level everywhere.

Traders may also look at the slope and shape of the TSI line. A rising line can suggest that momentum is building, while a flattening or turning line may suggest that momentum is easing.

Best TSI settings for different trading styles

The 25/13 setting is a common default, but it is not a rule. Shorter smoothing periods make the line more responsive, but they can also make it noisier. Longer smoothing periods make the line smoother, but they can make it slower to react.

Intraday trading

For day trading, traders working on lower timeframes may use shorter smoothing periods to respond sooner to changes in momentum. The trade-off is that the line may produce more false turns, because less smoothing allows more short-term noise through. Some traders compare these signals with a higher timeframe for extra context.

Swing trading

For swing trading, the classic 25/13 setting, often with a 7 or 13-period signal line, is a common middle ground for multi-day trading. It aims to balance responsiveness with noise reduction and usually produces fewer signals than very short settings.

Position and longer-term trading

For position trading, longer smoothing creates a slower TSI line that filters out more short-term movement. This may suit traders looking at the broader momentum backdrop of an asset, such as a major index. The trade-off is that turns may appear later.

Core TSI trading strategies

Traders use the TSI in several common ways to assess momentum. These approaches show how signals are often interpreted, rather than telling anyone how to trade. Like all momentum indicators, the TSI can produce false or delayed signals.

• Zero-line crossover. When the TSI moves from below zero to above zero, it may suggest momentum is shifting positive. A move from above zero to below zero may suggest momentum is turning negative.
• Signal-line crossover. When the TSI crosses above its signal line, short-term momentum may be strengthening. When it crosses below, momentum may be easing. Because the signal line lags the TSI, the move may already be underway.
• Overbought and oversold context. A stretched positive or negative reading can suggest a move has developed quickly, but it doesn’t mean price must reverse. In strong trends, the TSI can remain stretched for some time.
• Trend-line breaks on the oscillator. Some traders draw trend lines on the TSI itself and watch for breaks, as momentum changes may appear before they’re clear on the price chart.

These strategies are usually more useful when read alongside price structure and trend context. Signals can be unreliable, especially in ranging or low-volatility markets. Past performance is not a reliable indicator of future results.

TSI divergence strategy

Divergence is a common way to use the TSI because its smoother line can make momentum shifts easier to spot. It happens when price and the TSI move in different ways.

1. Bullish divergence: price makes a lower low, while the TSI makes a higher low. Some traders read this as a sign that selling momentum may be easing, but it doesn’t confirm a reversal.
2. Bearish divergence: price makes a higher high, while the TSI makes a lower high. This may suggest buying momentum is fading beneath a rising price.
3. Hidden bullish divergence: price makes a higher low in an uptrend, while the TSI makes a lower low. Some traders use this to assess whether the uptrend may continue.
4. Hidden bearish divergence: price makes a lower high in a downtrend, while the TSI makes a higher high. This may suggest the downtrend still has support.

Divergence can last for some time before price responds, if it responds at all. Many traders treat it as a warning that momentum may be changing, rather than as a precise timing tool. Past performance is not a reliable indicator of future results.

Combining the TSI with other indicators

Momentum indicators are often more useful when combined with tools that measure something different. The examples below show how traders may add context.

TSI with moving averages

A moving average on price can help show the broader trend. For example, a trader might pay closer attention to a bullish TSI cross when price is above a rising long-term moving average, and apply the reverse logic in a downtrend. In this type of setup, the moving average gives trend context, while the TSI shows momentum.

TSI with support and resistance

Support and resistance levels can add useful context to TSI signals. For example, bearish TSI divergence near a known resistance area may be more notable than the same divergence in the middle of a range. Bullish divergence near support may be viewed in a similar way. This does not confirm a move, but it can help traders assess whether a signal appears near an important price area.

TSI with the RSI

The relative strength index (RSI) is another momentum oscillator, but it reacts faster than the TSI because it is not double-smoothed in the same way. Some traders compare the two to see whether a faster momentum signal and a slower momentum signal are pointing in a similar direction. Because both indicators measure momentum, this is a cross-check rather than independent confirmation.

TSI with volume

Volume measures participation rather than momentum, so it can add a different type of information. A TSI turn that appears alongside rising volume may suggest broader market involvement. A similar turn on low volume may be treated more cautiously.

Risk management with the TSI

The TSI describes momentum; it does not manage risk. Its signals can be false, especially in ranging or low-volatility markets, so traders who use it often treat it as one input among several.

False crosses around the zero line are common when an asset is moving sideways. Divergence can also continue for some time before price reacts, if it reacts at all.

A risk-aware approach may include:

• Checking the wider trend before interpreting a signal.
• Comparing the TSI with price structure, support and resistance, or volume.
• Using predefined exit levels where appropriate.
• Keeping position size aligned with account risk.
• Testing settings on a demo account before using capital.

Position sizing and predefined exit levels matter regardless of what the indicator shows. Where a trader uses stop-loss orders, placement is often informed by price structure, such as a recent swing level, rather than by the oscillator itself. Standard stop-loss orders are not guaranteed. Guaranteed stop-loss orders incur a fee if activated.

A TSI reading may carry more weight when it lines up with the broader trend, key price levels and volume. It may carry less weight when it stands alone.

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