# Percent Change (PCTCHANGE)

> StratForge indicator page for change relative to a prior bar.

**Route**: `/indicators/pctchange/`

## What It Does

`stratforge::PctChange` compares the current input with the value `period` bars earlier. Its output is a **decimal ratio**, not a number already multiplied by 100. Multiply by 100 only when displaying a percentage.

## Formula and worked example

`PctChange(t) = Price(t) / Price(t - period) - 1`

For `period = 2`, input closes `[100, 105, 120]` produce `(120 / 100) - 1 = 0.20`, displayed as `20%`. The first two bars have no value because the earlier comparison bar is unavailable. With the default `period = 30`, the first value needs 31 bars.

If the comparison price is zero, the implementation performs division without a special zero-denominator rule; the result can be non-finite. Check input data before using the value in a signal. A zero period compares the bar with itself and yields zero for nonzero prices.

## Parameters

- `period` — lookback offset in bars; default `30`.

## C++23 API

```cpp
#include <stratforge/indicators/percentchange.hpp>
auto pctChange = std::make_unique<stratforge::PctChange>(data().close(), 30);
```

The example assumes a StratForge strategy with `data()` available and `<memory>` included. [Checked implementation](https://github.com/StratCraftsAI/StratForge/blob/d25404dcf2c3842ba304ddc60ac19cfec1f8aa37/include/stratforge/indicators/percentchange.hpp) (revision `d25404d`, 2026-08-28).

## Common Usage

- Compare changes across assets with different price scales after checking for zero and missing inputs.
- Pair the reading with trend or volatility context; the reading alone does not establish a trading edge.