Add inflation adjustment starter data

README.md

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+
+Inflation Adjusting
+
+`inflation-adjusting/main.py` sketches CPI-adjusted comparisons for policy limits like FDIC deposit insurance coverage and retirement contribution caps.

inflation-adjusting/README.md

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+# Inflation Adjusting
+
+Small starter dataset and script for comparing nominal policy limits in current dollars. This covers the two examples from issue #24:
+
+- FDIC standard maximum deposit insurance limits
+- 401(k) elective deferral and IRA contribution limits
+
+The script uses the `cpi` package from `palewire/cpi`, which adjusts U.S. dollars with CPI-U data.
+
+## Sources
+
+- FDIC, `Options for Deposit Insurance Reform`, Section 3, Table 3.1: standard maximum deposit insurance amount history.
+- IRS retirement topics and COLA pages for 2023-2026 401(k), 457(b), SIMPLE, and IRA limits.
+- `palewire/cpi` documentation for `cpi.inflate(amount, year, to=...)`.
+
+## Usage
+
+```console
+python -m pip install cpi
+python -m cpi update
+python inflation-adjusting/main.py --to-year 2026
+```
+
+Use `--category fdic` or `--category retirement` to print one group.

inflation-adjusting/main.py

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+"""Print nominal policy limits and CPI-adjusted comparisons."""
+
+from __future__ import annotations
+
+import argparse
+import csv
+import sys
+from dataclasses import dataclass
+from typing import Iterable
+
+
+@dataclass(frozen=True)
+class Limit:
+    category: str
+    name: str
+    year: int
+    amount: int
+    note: str
+
+
+# FDIC source: Options for Deposit Insurance Reform, Section 3, Table 3.1.
+FDIC_LIMITS = (
+    Limit("fdic", "temporary deposit insurance limit", 1934, 2500, "temporary 1934 limit"),
+    Limit("fdic", "standard deposit insurance limit", 1934, 5000, "permanent 1934 limit"),
+    Limit("fdic", "standard deposit insurance limit", 1950, 10000, ""),
+    Limit("fdic", "standard deposit insurance limit", 1966, 15000, ""),
+    Limit("fdic", "standard deposit insurance limit", 1969, 20000, ""),
+    Limit("fdic", "standard deposit insurance limit", 1974, 40000, ""),
+    Limit("fdic", "standard deposit insurance limit", 1980, 100000, ""),
+    Limit("fdic", "standard deposit insurance limit", 2008, 250000, ""),
+)
+
+
+# IRS retirement topics/COLA pages for recent contribution limits.
+RETIREMENT_LIMITS = (
+    Limit("retirement", "401(k), 403(b), and 457(b) elective deferral", 2023, 22500, ""),
+    Limit("retirement", "401(k), 403(b), and 457(b) elective deferral", 2024, 23000, ""),
+    Limit("retirement", "401(k), 403(b), and 457(b) elective deferral", 2025, 23500, ""),
+    Limit("retirement", "401(k), 403(b), and 457(b) elective deferral", 2026, 24500, ""),
+    Limit("retirement", "traditional and Roth IRA contribution", 2023, 6500, ""),
+    Limit("retirement", "traditional and Roth IRA contribution", 2024, 7000, ""),
+    Limit("retirement", "traditional and Roth IRA contribution", 2025, 7000, ""),
+    Limit("retirement", "traditional and Roth IRA contribution", 2026, 7500, ""),
+    Limit("retirement", "SIMPLE plan elective deferral", 2023, 15500, ""),
+    Limit("retirement", "SIMPLE plan elective deferral", 2024, 16000, ""),
+    Limit("retirement", "SIMPLE plan elective deferral", 2025, 16500, ""),
+    Limit("retirement", "SIMPLE plan elective deferral", 2026, 17000, ""),
+)
+
+
+def selected_limits(category: str) -> Iterable[Limit]:
+    if category == "fdic":
+        return FDIC_LIMITS
+    if category == "retirement":
+        return RETIREMENT_LIMITS
+    return (*FDIC_LIMITS, *RETIREMENT_LIMITS)
+
+
+def inflate(amount: int, year: int, to_year: int | None) -> float:
+    try:
+        import cpi
+    except ImportError as exc:
+        raise SystemExit(
+            "Install CPI data support first: python -m pip install cpi"
+        ) from exc
+
+    if to_year is None:
+        return cpi.inflate(amount, year)
+    return cpi.inflate(amount, year, to=to_year)
+
+
+def parse_args(argv: list[str] | None = None) -> argparse.Namespace:
+    parser = argparse.ArgumentParser(
+        description="Print CPI-adjusted FDIC and retirement policy limits."
+    )
+    parser.add_argument(
+        "--category",
+        choices=("all", "fdic", "retirement"),
+        default="all",
+        help="Limit output to one dataset.",
+    )
+    parser.add_argument(
+        "--to-year",
+        type=int,
+        default=None,
+        help="Adjustment year. Defaults to the latest CPI year available.",
+    )
+    return parser.parse_args(argv)
+
+
+def main(argv: list[str] | None = None) -> int:
+    args = parse_args(argv)
+    writer = csv.writer(sys.stdout)
+    writer.writerow(
+        ("category", "name", "year", "nominal_amount", "to_year", "adjusted_amount", "note")
+    )
+    for item in selected_limits(args.category):
+        writer.writerow(
+            (
+                item.category,
+                item.name,
+                item.year,
+                item.amount,
+                args.to_year or "latest",
+                round(inflate(item.amount, item.year, args.to_year), 2),
+                item.note,
+            )
+        )
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())