---
title: Data Transformations Reference
description: Complete reference for FRED data transformations
icon: 'calculator'
---
# 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>
