> ## Documentation Index
> Fetch the complete documentation index at: https://fred-mcp-server.amorelli.tech/llms.txt
> Use this file to discover all available pages before exploring further.

# Data Transformations Reference

> Complete reference for FRED data transformations

# Data Transformations Reference

Quick reference guide for all available FRED data transformations.

## Transformation Codes

| Code | Name         | Formula                      | Use Case      |
| ---- | ------------ | ---------------------------- | ------------- |
| lin  | Levels       | x\_t                         | Raw values    |
| chg  | Change       | x\_t - x\_{t-1}              | Period change |
| ch1  | Change YoY   | x\_t - x\_{t-n}              | Annual change |
| pch  | % Change     | ((x\_t/x\_{t-1})-1)\*100     | Growth rate   |
| pc1  | % Change YoY | ((x\_t/x\_{t-n})-1)\*100     | Annual growth |
| pca  | Annual Rate  | (((x\_t/x\_{t-1})^n)-1)\*100 | Annualized    |
| cch  | Log Change   | (ln(x\_t)-ln(x\_{t-1}))\*100 | Log returns   |
| cca  | Log Annual   | (ln(x\_t)-ln(x\_{t-n}))\*100 | Annual log    |
| log  | Natural Log  | ln(x\_t)                     | Log levels    |

## Selection Guide

### By Data Type

**Flow Variables** (rates, prices):

* Use: pch, pc1, pca
* Example: Inflation, interest rates

**Stock Variables** (levels, balances):

* Use: chg, ch1
* Example: Employment, inventories

**Financial Returns**:

* Use: cch, log
* Example: Stock prices, exchange rates

## Common Mistakes

❌ **Don't:**

* Transform already-transformed series
* Mix frequencies when comparing
* Ignore seasonal adjustment

✅ **Do:**

* Check original units
* Use consistent transformations
* Document your choices

## Next Steps

<CardGroup cols={2}>
  <Card title="Examples" icon="code" href="/examples/data-transformations">
    Practical examples
  </Card>

  <Card title="API Reference" icon="book" href="/api-reference/fred-get-series">
    API documentation
  </Card>
</CardGroup>