Index IRS parameters to the 12-months-ending-August chained CPI-U, with CBO's tax-year projections

changelog.d/irs-index-tax-year-cpi.fixed.md

@@ -0,0 +1 @@
+Correct IRS September–August inflation windows and separate CBO tax-year projections while preserving published amounts; calculate dependent deduction limits from statutory bases, separate Vermont and Wisconsin unchained CPI schedules, preserve CBO calendar forecast anchors, and encode published 2026 Wisconsin and California tax amounts. Update observed chained and seasonally adjusted CPI-U through August 2026.

policyengine_us/parameters/gov/bls/cpi/c_cpi_u.yaml

@@ -320,25 +320,27 @@ values:
   2026-04-01: 184.499
   2026-05-01: 185.589
   2026-06-01: 184.992
-  # CBO projections from CBO Feb 2026 forecast for future periods.
-  # CBO projects the average C-CPI-U over the 12mo ending August,
-  # which determines tax parameters for the following year.
-  2027-02-01: 187.2 # 2028 value.
-  2028-02-01: 191.1 # 2029 value.
-  2029-02-01: 194.9 # 2030 value.
-  2030-02-01: 198.8 # 2031 value.
-  2031-02-01: 202.7 # 2032 value.
-  2032-02-01: 206.7 # 2033 value.
-  2033-02-01: 210.8 # 2034 value.
-  2034-02-01: 214.9 # 2035 value.
-  2035-02-01: 219.2 # 2036 value.
+  2026-07-01: 185.162
+  2026-08-01: 185.739
+  # CBO's February 2026 projections of each calendar year's average C-CPI-U.
+  # Tax parameters use the average over the 12 months ending August instead;
+  # CBO's projections of that average are in tax_year_projection/c_cpi_u.yaml.
+  2027-02-01: 187.2 # Calendar year 2027 average.
+  2028-02-01: 191.1 # Calendar year 2028 average.
+  2029-02-01: 194.9 # Calendar year 2029 average.
+  2030-02-01: 198.8 # Calendar year 2030 average.
+  2031-02-01: 202.7 # Calendar year 2031 average.
+  2032-02-01: 206.7 # Calendar year 2032 average.
+  2033-02-01: 210.8 # Calendar year 2033 average.
+  2034-02-01: 214.9 # Calendar year 2034 average.
+  2035-02-01: 219.2 # Calendar year 2035 average.
   # Values for 2036-2100 are set programmatically in uprating_extensions.py
 metadata:
   economy: false
   unit: currency-USD
   label: Chained CPI-U
   reference:
-    - title: BLS | Chained CPI-U, U.S. city average, all items (SUUR0000SA0), monthly values through June 2026
+    - title: BLS | Chained CPI-U, U.S. city average, all items (SUUR0000SA0), monthly values through August 2026
       href: https://data.bls.gov/timeseries/SUUR0000SA0
     - title: CBO | Tax Parameters and Effective Marginal Tax Rates | June 2024
       # Source: https://www.cbo.gov/data/budget-economic-data#10

policyengine_us/parameters/gov/bls/cpi/cpi_u.yaml

@@ -1363,23 +1363,27 @@ values:
   2026-04-01: 332.407
   2026-05-01: 333.979
   2026-06-01: 332.568
-  # CBO projections from CBO Feb 2026 forecast for future periods.
-  2027-02-01: 340.3 # 2028 value.
-  2028-02-01: 348.3 # 2029 value.
-  2029-02-01: 356.3 # 2030 value.
-  2030-02-01: 364.3 # 2031 value.
-  2031-02-01: 372.6 # 2032 value.
-  2032-02-01: 381.0 # 2033 value.
-  2033-02-01: 389.6 # 2034 value.
-  2034-02-01: 398.4 # 2035 value.
-  2035-02-01: 407.3 # 2036 value.
+  2026-07-01: 332.813
+  2026-08-01: 334.131
+  # CBO's February 2026 projections of each calendar year's average CPI-U.
+  # Tax parameters use the average over the 12 months ending August instead;
+  # CBO's projections of that average are in tax_year_projection/cpi_u.yaml.
+  2027-02-01: 340.3 # Calendar year 2027 average.
+  2028-02-01: 348.3 # Calendar year 2028 average.
+  2029-02-01: 356.3 # Calendar year 2029 average.
+  2030-02-01: 364.3 # Calendar year 2030 average.
+  2031-02-01: 372.6 # Calendar year 2031 average.
+  2032-02-01: 381.0 # Calendar year 2032 average.
+  2033-02-01: 389.6 # Calendar year 2033 average.
+  2034-02-01: 398.4 # Calendar year 2034 average.
+  2035-02-01: 407.3 # Calendar year 2035 average.
   # Values for 2036-2100 are set programmatically in uprating_extensions.py
 metadata:
   unit: currency-USD
   label: CPI-U
   economy: false
   reference:
-    - title: BLS | CPI-U, U.S. city average, all items, seasonally adjusted (CUSR0000SA0), monthly values through June 2026
+    - title: BLS | CPI-U, U.S. city average, all items, seasonally adjusted (CUSR0000SA0), monthly values through August 2026
       href: https://data.bls.gov/timeseries/CUSR0000SA0
     - title: CBO | Tax Parameters and Effective Marginal Tax Rates | June 2024
       # Source: https://www.cbo.gov/data/budget-economic-data#10