# U.S. Inflation (CPI): Executive Summary

---

## 🎯 BEST ESTIMATE

| Metric | Value | Confidence | Last Updated |
|--------|-------|------------|--------------|
| **CPI-U Index (August 2025)** | **323.4** | 99% | October 2025 |
| **Year-over-Year Inflation** | **~2.5%** | 99% | October 2025 |
| **Fed Target** | **2.0%** | Reference | - |

**One-liner:** U.S. inflation is ~2.5% (YoY), with CPI index at 323.4 (1982-84=100 baseline).

**Caveat:** CPI measures urban consumers only (~93% of population); regional variation may differ significantly.

---

## The Big Picture

The [Consumer Price Index (CPI)](https://www.bls.gov/cpi/) is the primary measure of inflation in the United States—tracking changes in the price level of a basket of consumer goods and services. The [Bureau of Labor Statistics (BLS)](https://www.bls.gov/) produces this data monthly.

**What the current numbers mean:**
- A CPI of 323.4 means that goods costing $100 in 1982-84 now cost $323.40
- At 2.5% annual inflation, prices double approximately every 28 years
- Current inflation is near the [Federal Reserve's 2% target](https://www.federalreserve.gov/faqs/economy_14400.htm)

---

## Why This Number Matters

Inflation affects virtually every economic decision:

- **Wages**: [Cost-of-living adjustments (COLAs)](https://www.ssa.gov/oact/cola/colaseries.html) are tied to CPI
- **Savings**: Determines whether your money gains or loses purchasing power
- **Interest Rates**: The [Federal Reserve](https://www.federalreserve.gov/) adjusts rates based on inflation
- **Contracts**: Many business and government contracts escalate with CPI
- **Policy**: Trillions in Social Security, Medicare, and tax brackets adjust with CPI

A [1% change in CPI](https://www.bls.gov/cpi/) affects billions of dollars in annual adjustments.

---

## Current Data Highlights

### Recent Readings
| Period | CPI Index | YoY Inflation | Source |
|--------|-----------|---------------|--------|
| August 2025 | [323.4](https://fred.stlouisfed.org/series/CPIAUCSL) | ~2.5% | [BLS](https://www.bls.gov/cpi/) |
| June 2022 | 296.3 | 9.1% (peak) | [BLS](https://www.bls.gov/cpi/) |
| 1982-84 Avg | 100.0 | Baseline | [BLS](https://www.bls.gov/cpi/) |
| January 1947 | 21.5 | First obs. | [BLS](https://www.bls.gov/cpi/) |

### Long-Term Trend
| Period | Average Annual Inflation |
|--------|-------------------------|
| 1947-2025 (Full) | ~3.5% |
| 1990-2019 (Pre-COVID) | ~2.4% |
| 2021-2023 (COVID Surge) | ~6.0% |
| 2024-2025 (Current) | ~2.5% |

---

## How the Number Is Calculated

The BLS uses a [Laspeyres price index](https://www.bls.gov/opub/hom/cpi/calculation.htm):

**CPI = (Cost of basket today / Cost of basket in base period) × 100**

### The Market Basket
| Category | Weight | Examples |
|----------|--------|----------|
| **Housing** | ~34% | Rent, utilities, furnishings |
| **Food** | ~14% | Groceries, restaurants |
| **Transportation** | ~16% | Vehicles, gas, insurance |
| **Medical Care** | ~9% | Healthcare, drugs, insurance |
| **Recreation** | ~5% | Entertainment, sports, hobbies |
| **Education/Communication** | ~7% | Tuition, phones, internet |
| **Other** | ~15% | Apparel, personal care |

**Data Collection:**
- ~80,000 prices collected monthly
- 75 urban areas across the U.S.
- Weights updated every 2 years from [Consumer Expenditure Survey](https://www.bls.gov/cex/)

---

## Key Inflation Rates to Know

| Measure | What It Is | FRED ID |
|---------|-----------|---------|
| **Headline CPI** | All items | [CPIAUCSL](https://fred.stlouisfed.org/series/CPIAUCSL) |
| **Core CPI** | Excludes food & energy | [CPILFESL](https://fred.stlouisfed.org/series/CPILFESL) |
| **PCE** | Fed's preferred measure | [PCEPI](https://fred.stlouisfed.org/series/PCEPI) |
| **Core PCE** | Fed's key target | [PCEPILFE](https://fred.stlouisfed.org/series/PCEPILFE) |

**Why Core?** Food and energy prices are volatile. Core inflation shows underlying trends.

**Why PCE?** The Federal Reserve targets [PCE inflation](https://fred.stlouisfed.org/series/PCEPI) rather than CPI because it accounts for substitution effects.

---

## Historical Inflation Episodes

| Period | Peak Inflation | Cause |
|--------|---------------|-------|
| [1970s Stagflation](https://fred.stlouisfed.org/series/CPIAUCSL) | 14.8% (1980) | Oil shocks, monetary policy |
| [Volcker Shock](https://www.federalreserve.gov/aboutthefed/bios/board/volcker.htm) | Fed raised rates to 20%+ | Broke inflation cycle |
| [Great Moderation](https://www.federalreserve.gov/pubs/ifdp/2005/835/default.htm) | 2-3% (1990s-2000s) | Credible monetary policy |
| [Great Recession](https://fred.stlouisfed.org/series/CPIAUCSL) | Brief deflation (2009) | Financial crisis |
| [COVID Surge](https://fred.stlouisfed.org/series/CPIAUCSL) | 9.1% (June 2022) | Supply chain, stimulus |
| **Current** | ~2.5% (2025) | Fed tightening working |

---

## Confidence Assessment

| Component | Confidence | Explanation |
|-----------|------------|-------------|
| **Current CPI Index** | 99% | Official government statistic, gold standard |
| **YoY Inflation Rate** | 99% | Direct calculation from CPI data |
| **Historical Data** | 99%+ | Fully verified, minimal revisions |

This is the most reliable inflation data available—produced by the U.S. government with rigorous methodology and complete transparency.

---

## Known Limitations

1. **Substitution bias**: Fixed basket doesn't fully capture when consumers switch to cheaper alternatives
2. **Quality adjustment**: Hard to account for product quality improvements over time
3. **New products**: Slow to incorporate new goods (smartphones took years)
4. **Geographic variation**: National average masks significant regional differences
5. **Population**: Covers urban consumers only (~93% of U.S.)

---

## How to Calculate Inflation

### Year-over-Year Rate
```
Inflation Rate = ((CPI_now - CPI_1year_ago) / CPI_1year_ago) × 100
```

### Convert Dollars Across Time
```
Real_value = Nominal_value × (CPI_target_year / CPI_original_year)
```

Example: $100 in 1984 equals ~$323 in 2025 purchasing power.

---

## Data Sources

| Source | What It Provides | Link |
|--------|-----------------|------|
| [Bureau of Labor Statistics](https://www.bls.gov/cpi/) | Official CPI (primary authority) | [CPI Home](https://www.bls.gov/cpi/) |
| [FRED](https://fred.stlouisfed.org/) | Easy API access to BLS data | [CPIAUCSL](https://fred.stlouisfed.org/series/CPIAUCSL) |

**Quick Access:**
```bash
# Download latest CPI data from FRED
curl -L "https://fred.stlouisfed.org/graph/fredgraph.csv?id=CPIAUCSL" -o CPI-latest.csv
```

---

## Supporting Documentation

| Document | Description |
|----------|-------------|
| [US-Inflation-CPI-1947-2025.md](./US-Inflation-CPI-1947-2025.md) | Full dataset documentation |
| [source.md](./source.md) | Detailed methodology |
| [CPI-US-Monthly-1947-2025.csv](./CPI-US-Monthly-1947-2025.csv) | Monthly data (945 observations) |

---

## Research Metadata

| Attribute | Value |
|-----------|-------|
| **Research Date** | October 2025 |
| **Researcher** | Kai |
| **Method** | Direct BLS/FRED data collection |
| **Confidence Level** | 99% (official government statistic) |
| **Known Gaps** | Pre-1947 data uses different methodology |

---

## Changelog

| Date | Change | Reason |
|------|--------|--------|
| **December 2025** | Added SUMMARY.md with executive overview | Standardizing Substrate datasets to "Answer First" schema |
| **October 2025** | Initial dataset creation | Comprehensive U.S. CPI data collection |

---

## External Resources

- [BLS CPI FAQ](https://www.bls.gov/cpi/questions-and-answers.htm) - Common questions
- [BLS Handbook of Methods](https://www.bls.gov/opub/hom/cpi/) - Full methodology
- [Fed Inflation Target](https://www.federalreserve.gov/faqs/economy_14400.htm) - Why 2%?
- [CPI Inflation Calculator](https://www.bls.gov/data/inflation_calculator.htm) - BLS tool