---
title: "True Strength Index"
description: "This indicator computes the True Strength Index (TSI). The True Strength Index is calculated as explained here: https://school...."
canonical: https://www.quantconnect.com/docs/v2/writing-algorithms/indicators/supported-indicators/true-strength-index
markdown: https://www.quantconnect.com/docs/v2/writing-algorithms/indicators/supported-indicators/true-strength-index.md
language: python
source: https://github.com/QuantConnect/Documentation/tree/master/03%20Writing%20Algorithms/28%20Indicators/01%20Supported%20Indicators/118%20True%20Strength%20Index
modified: 2026-10-30
index: https://www.quantconnect.com/llms.txt
---

# True Strength Index

[Documentation](https://www.quantconnect.com/docs/v2.md) > [Writing Algorithms](https://www.quantconnect.com/docs/v2/writing-algorithms.md) > Indicators > [Supported Indicators](https://www.quantconnect.com/docs/v2/writing-algorithms/indicators/supported-indicators.md) > True Strength Index

> Code examples are shown in Python. Append `?lang=csharp` to this URL for the C# version of this page.

## Introduction

This indicator computes the True Strength Index (TSI). The True Strength Index is calculated as explained here: https://school.stockcharts.com/doku.php?id=technical_indicators:True_strength_index Briefly, the calculation has three steps: 1. Smooth the momentum and the absolute momentum by getting an EMA of them (typically of period 25) 2. Double smooth the momentum and the absolute momentum by getting an EMA of their EMA (typically of period 13) 3. The TSI formula itself: divide the double-smoothed momentum over the double-smoothed absolute momentum and multiply by 100 The signal is typically a 7-to-12-EMA of the TSI.

To view the implementation of this indicator, see the [LEAN GitHub repository](https://github.com/QuantConnect/Lean/tree/master/Indicators/TrueStrengthIndex.cs).

## Using TSI Indicator

To create an automatic indicator for `TrueStrengthIndex`, call the `tsi` helper method from the `QCAlgorithm` class. The `tsi` method creates a `TrueStrengthIndex` object, hooks it up for automatic updates, and returns it so you can used it in your algorithm. In most cases, you should call the helper method in the `initialize` method.

```python
class TrueStrengthIndexAlgorithm(QCAlgorithm):
    def initialize(self) -> None:
        self._symbol = self.add_equity("SPY", Resolution.DAILY).symbol
        self._tsi = self.tsi(self._symbol, 25, 13, 7, MovingAverageType.EXPONENTIAL)

    def on_data(self, slice: Slice) -> None:

        if self._tsi.is_ready:
            # The current value of self._tsi is represented by self._tsi.current.value
            self.plot("TrueStrengthIndex", "tsi", self._tsi.current.value)
            # Plot all attributes of self._tsi
            self.plot("TrueStrengthIndex", "signal", self._tsi.signal.current.value)
```

For more information about this method, see the [QCAlgorithm class](https://www.lean.io/docs/v2/lean-engine/class-reference/py/QuantConnect/Algorithm/QCAlgorithm/#QuantConnect.Algorithm.QCAlgorithm.tsi).

You can manually create a `TrueStrengthIndex` indicator, so it doesn't automatically update. Manual indicators let you update their values with any data you choose.

Updating your indicator manually enables you to control when the indicator is updated and what data you use to update it. To manually update the indicator, call the `update` method. The indicator will only be ready after you prime it with enough data.

```python
class TrueStrengthIndexAlgorithm(QCAlgorithm):
    def initialize(self) -> None:
        self._symbol = self.add_equity("SPY", Resolution.DAILY).symbol
        self._truestrengthindex = TrueStrengthIndex(25, 13, 7, MovingAverageType.EXPONENTIAL)

    def on_data(self, slice: Slice) -> None:
        bar = slice.bars.get(self._symbol)
        if bar:
            self._truestrengthindex.update(bar.end_time, bar.close)

        if self._truestrengthindex.is_ready:
            # The current value of self._truestrengthindex is represented by self._truestrengthindex.current.value
            self.plot("TrueStrengthIndex", "truestrengthindex", self._truestrengthindex.current.value)
            # Plot all attributes of self._truestrengthindex
            self.plot("TrueStrengthIndex", "signal", self._truestrengthindex.signal.current.value)
```

For more information about this indicator, see its [reference](https://www.lean.io/docs/v2/lean-engine/class-reference/py/QuantConnect/Indicators/TrueStrengthIndex).

## Visualization

The following plot shows values for some of the `TrueStrengthIndex` indicator properties:

![TrueStrengthIndex line plot.](https://cdn.quantconnect.com/docs/i/writing-algorithms/indicators/supported-indicators/true-strength-index.png)

## Indicator History

To get the historical data of the `TrueStrengthIndex` indicator, call the `self.indicator_history` method. This method resets your indicator, makes a [history request](https://www.quantconnect.com/docs/v2/writing-algorithms/historical-data/history-requests.md), and updates the indicator with the historical data. Just like with regular history requests, the `indicator_history` method supports time periods based on a trailing number of bars, a trailing period of time, or a defined period of time. If you don't provide a `resolution` argument, it defaults to match the resolution of the security subscription.

```python
class TrueStrengthIndexAlgorithm(QCAlgorithm):
    def initialize(self) -> None:
        self._symbol = self.add_equity("SPY", Resolution.DAILY).symbol
        self._tsi = self.tsi(self._symbol, 25, 13, 7, MovingAverageType.EXPONENTIAL)

        indicator_history = self.indicator_history(self._tsi, self._symbol, 100, Resolution.MINUTE)
        timedelta_indicator_history = self.indicator_history(self._tsi, self._symbol, timedelta(days=10), Resolution.MINUTE)
        time_period_indicator_history = self.indicator_history(self._tsi, self._symbol, datetime(2024, 7, 1), datetime(2024, 7, 5), Resolution.MINUTE)

        # Access all attributes of indicator_history
        indicator_history_df = indicator_history.data_frame
        signal = indicator_history_df["signal"]
```