MaxGhenis · Oct 10, 2026 · Sep 27, 2026 · Oct 2, 2026 · Oct 2, 2026 · Oct 2, 2026
diff --git a/changelog.d/1887.fixed.md b/changelog.d/1887.fixed.md
@@ -0,0 +1 @@
+- Fix Class 2 National Insurance for 2015-16 to 2023-24 against s.11 SSCBA 1992: charge £3.45 a week in 2023-24; from 2022-23 charge only profits above the Class 2 lower profits threshold (£11,908, then £12,570), with profits from the small profits threshold up to it treated as paid; keep the small profits threshold at £6,725 in 2023-24 and 2024-25 and correct it to £5,965 in 2015-16 and 2016-17; date the abolition 6 April 2024. Class 2 now tests its thresholds on the profits Class 4 is charged on (s.11(3)), after capital allowances, the trading allowance and loss relief, not on self-employment income. A full year of Class 2 is every contribution week in it, so 53 weeks in 2019-20. The Universal Credit minimum income floor's notional Class 2 follows the same rule, so it deducts no Class 2 in 2022-23 and 2023-24 on a threshold the lower profits threshold covers. Every value now cites its amending instrument.
diff --git a/changelog.d/1968.fixed.md b/changelog.d/1968.fixed.md
@@ -0,0 +1 @@
+- Fixed Class 4 NICs against s.15 SSCBA 1992: the 2023-24 lower profits limit is £12,570 (it was £11,908), the 2022-23 rates are 9.73% and 2.73% for the whole year (they were 10.25% and 3.5%), the 2023-24 additional rate is 2% (it was 3.5%), and the 2015-16 upper profits limit is £42,385. Every Class 4 limit and rate from 2015-16 to 2025-26 now cites its legal source.
diff --git a/docs/book/policy/model-baseline.md b/docs/book/policy/model-baseline.md
@@ -28,7 +28,7 @@ Annual benefit uprating applied 4.1% increases to state pensions and 1.7% to wor
 
 ### Autumn Statement 2023
 
-The government announced further National Insurance cuts, reducing the [employee main rate from 10% to 8%](https://github.com/PolicyEngine/policyengine-uk/blob/master/policyengine_uk/parameters/gov/hmrc/national_insurance/class_1/rates/employee/main.yaml#L24-L29) and the [self-employed Class 4 rate from 9% to 6%](https://github.com/PolicyEngine/policyengine-uk/blob/master/policyengine_uk/parameters/gov/hmrc/national_insurance/class_4/rates/main.yaml#L16-L21) in fiscal year 2024-25. [Class 2 National Insurance contributions were abolished](https://github.com/PolicyEngine/policyengine-uk/blob/master/policyengine_uk/parameters/gov/hmrc/national_insurance/class_2/flat_rate.yaml#L14-L19) for self-employed people, with the flat rate set to £0 in fiscal year 2024-25.
+The government announced further National Insurance cuts, reducing the [employee main rate from 10% to 8%](https://github.com/PolicyEngine/policyengine-uk/blob/master/policyengine_uk/parameters/gov/hmrc/national_insurance/class_1/rates/employee/main.yaml#L24-L29) and the [self-employed Class 4 rate from 9% to 6%](https://github.com/PolicyEngine/policyengine-uk/blob/master/policyengine_uk/parameters/gov/hmrc/national_insurance/class_4/rates/main.yaml#L26-L33) in fiscal year 2024-25. [Class 2 National Insurance contributions were abolished](https://github.com/PolicyEngine/policyengine-uk/blob/master/policyengine_uk/parameters/gov/hmrc/national_insurance/class_2/flat_rate.yaml#L51-L56) for self-employed people, with the flat rate set to £0 in fiscal year 2024-25.
 
 ### Capital gains tax changes (Autumn Budget 2024)
 

diff --git a/docs/book/programs/gov/hmrc/national-insurance.ipynb b/docs/book/programs/gov/hmrc/national-insurance.ipynb
diff --git a/policyengine_uk/parameters/gov/hmrc/national_insurance/class_2/flat_rate.yaml b/policyengine_uk/parameters/gov/hmrc/national_insurance/class_2/flat_rate.yaml
@@ -1,25 +1,65 @@
-description: Flat rate National Insurance contribution for self-employed earners.
+description: Weekly Class 2 National Insurance contribution that self-employed earners are liable to pay under section 11(2) of the Social Security Contributions and Benefits Act 1992. Compulsory Class 2 ended on 6 April 2024; voluntary Class 2 is not modelled.
 values:
-  2015-04-01: 2.8
-  2017-04-01: 2.85
-  2018-04-01: 2.95
-  2019-04-01: 3
-  2020-04-01: 3.05
+  2015-04-06:
+    value: 2.8
+    metadata:
+      reference:
+        - title: National Insurance Contributions Act 2015 Sch 1 para 3 (substituting s 11(2) of the Social Security Contributions and Benefits Act 1992)
+          href: https://www.legislation.gov.uk/ukpga/2015/5/schedule/1/paragraph/3/enacted
+        - title: Social Security Contributions and Benefits Act 1992 s 11(2) (as at 6 April 2016, unchanged for 2016-17)
+          href: https://www.legislation.gov.uk/ukpga/1992/4/section/11/2016-04-06
+  2017-04-06:
+    value: 2.85
+    metadata:
+      reference:
+        - title: The Social Security (Contributions) (Rates, Limits and Thresholds Amendments and National Insurance Funds Payments) Regulations 2017 reg 3(a)
+          href: https://www.legislation.gov.uk/uksi/2017/415/regulation/3/made
+  2018-04-06:
+    value: 2.95
+    metadata:
+      reference:
+        - title: The Social Security (Contributions) (Rates, Limits and Thresholds Amendments and National Insurance Funds Payments) Regulations 2018 reg 3(a)
+          href: https://www.legislation.gov.uk/uksi/2018/337/regulation/3/made
+  2019-04-06:
+    value: 3
+    metadata:
+      reference:
+        - title: The Social Security (Contributions) (Rates, Limits and Thresholds Amendments and National Insurance Funds Payments) Regulations 2019 reg 3(a)
+          href: https://www.legislation.gov.uk/uksi/2019/262/regulation/3/made
+  2020-04-06:
+    value: 3.05
+    metadata:
+      reference:
+        - title: The Social Security (Contributions) (Rates, Limits and Thresholds Amendments and National Insurance Funds Payments) Regulations 2020 reg 3(a)
+          href: https://www.legislation.gov.uk/uksi/2020/299/regulation/3/made
+        - title: Social Security Contributions and Benefits Act 1992 s 11(2) (as at 6 April 2021, unchanged for 2021-22)
+          href: https://www.legislation.gov.uk/ukpga/1992/4/section/11/2021-04-06
   2022-04-06:
     value: 3.15
     metadata:
       reference:
-        - title: The Social Security (Contributions) (Rates, Limits and Thresholds Amendments and National Insurance Funds Payments) Regulations 2022(3)(a)
-          href: https://www.legislation.gov.uk/uksi/2022/232/regulation/3/made#regulation-3-a
-  2024-01-01:
+        - title: The Social Security (Contributions) (Rates, Limits and Thresholds Amendments and National Insurance Funds Payments) Regulations 2022 reg 3(a)
+          href: https://www.legislation.gov.uk/uksi/2022/232/regulation/3/made
+  2023-04-06:
+    value: 3.45
+    metadata:
+      reference:
+        - title: The Social Security (Contributions) (Rates, Limits and Thresholds Amendments and National Insurance Funds Payments) Regulations 2023 reg 3(a)
+          href: https://www.legislation.gov.uk/uksi/2023/236/regulation/3/made
+        - title: Social Security Contributions and Benefits Act 1992 s 11(2) (as at 6 April 2023)
+          href: https://www.legislation.gov.uk/ukpga/1992/4/section/11/2023-04-06
+  2024-04-06:
     value: 0
     metadata:
       reference:
-        - title: "Autumn Statement 2023: National Insurance Factsheet"
-          href: https://www.gov.uk/government/publications/autumn-statement-2023-national-insurance-factsheet/autumn-statement-2023-national-insurance-factsheet
+        - title: National Insurance Contributions (Reduction in Rates) Act 2023 s 3(1)(a) and (3) (omitting s 11(2) of the Social Security Contributions and Benefits Act 1992 from 6 April 2024)
+          href: https://www.legislation.gov.uk/ukpga/2023/57/section/3/enacted
 metadata:
   unit: currency-GBP
+  period: week
   label: NI class 2 flat rate
   reference:
-    - https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/882271/Table-a4.pdf
-    - https://www.gov.uk/government/publications/rates-and-allowances-national-insurance-contributions/rates-and-allowances-national-insurance-contributions
+    - title: Social Security Contributions and Benefits Act 1992 s 11
+      href: https://www.legislation.gov.uk/ukpga/1992/4/section/11
+    - title: "GOV.UK | Rates and allowances: National Insurance contributions"
+      href: https://www.gov.uk/government/publications/rates-and-allowances-national-insurance-contributions/rates-and-allowances-national-insurance-contributions
diff --git a/policyengine_uk/parameters/gov/hmrc/national_insurance/class_2/lower_profits_threshold.yaml b/policyengine_uk/parameters/gov/hmrc/national_insurance/class_2/lower_profits_threshold.yaml
@@ -0,0 +1,21 @@
+description: Lower profits threshold for Class 2 National Insurance contributions under section 11(4)(a) of the Social Security Contributions and Benefits Act 1992. In 2022-23 and 2023-24 self-employed earners were liable for Class 2 only on profits above it. Section 11(4)(a) was omitted from 6 April 2024, when compulsory Class 2 ended; the 2023-24 value applies to reforms that restore a Class 2 rate.
+values:
+  2022-04-06:
+    value: 11_908
+    metadata:
+      reference:
+        - title: The Social Security (Class 2 National Insurance Contributions Increase of Threshold) Regulations 2022 reg 2(3)
+          href: https://www.legislation.gov.uk/uksi/2022/1329/regulation/2/made
+  2023-04-06:
+    value: 12_570
+    metadata:
+      reference:
+        - title: The Social Security (Contributions) (Rates, Limits and Thresholds Amendments and National Insurance Funds Payments) Regulations 2023 reg 3(b)
+          href: https://www.legislation.gov.uk/uksi/2023/236/regulation/3/made
+metadata:
+  unit: currency-GBP
+  period: year
+  label: NI class 2 lower profits threshold
+  reference:
+    - title: Social Security Contributions and Benefits Act 1992 s 11(2), (4) and (5A) (as at 6 April 2023)
+      href: https://www.legislation.gov.uk/ukpga/1992/4/section/11/2023-04-06
diff --git a/...ne_uk/parameters/gov/hmrc/national_insurance/class_2/lower_profits_threshold_applies.yaml b/...ne_uk/parameters/gov/hmrc/national_insurance/class_2/lower_profits_threshold_applies.yaml
@@ -0,0 +1,21 @@
+description: Class 2 National Insurance liability starts above the lower profits threshold rather than at the small profits threshold. In 2022-23 and 2023-24 profits from the small profits threshold up to the lower profits threshold were treated as paid. Compulsory Class 2 ended on 6 April 2024; the switch stays on so that a reform restoring a Class 2 rate uses the 2023-24 rule.
+values:
+  2015-04-06:
+    value: false
+    metadata:
+      reference:
+        - title: Social Security Contributions and Benefits Act 1992 s 11(2) (as at 6 April 2021)
+          href: https://www.legislation.gov.uk/ukpga/1992/4/section/11/2021-04-06
+  2022-04-06:
+    value: true
+    metadata:
+      reference:
+        - title: The Social Security (Class 2 National Insurance Contributions Increase of Threshold) Regulations 2022 regs 1 and 2(2)
+          href: https://www.legislation.gov.uk/uksi/2022/1329/regulation/2/made
+metadata:
+  unit: bool
+  period: year
+  label: Class 2 liability starts above the lower profits threshold
+  reference:
+    - title: Social Security Contributions and Benefits Act 1992 s 11(2), (5A) and (5B) (as at 6 April 2023)
+      href: https://www.legislation.gov.uk/ukpga/1992/4/section/11/2023-04-06
diff --git a/policyengine_uk/parameters/gov/hmrc/national_insurance/class_2/small_profits_threshold.yaml b/policyengine_uk/parameters/gov/hmrc/national_insurance/class_2/small_profits_threshold.yaml
@@ -1,35 +1,80 @@
-description: Small profits National Insurance threshold for self-employed earners.
+description: Small profits threshold for Class 2 National Insurance contributions under section 11(4) of the Social Security Contributions and Benefits Act 1992. Before 2022-23 self-employed earners with profits at or above it were liable for Class 2; in 2022-23 and 2023-24 profits from this threshold up to the lower profits threshold were treated as paid.
 values:
-  2015-04-06: 3_965
-  2017-04-06: 6_025
-  2018-04-06: 6_205
-  2019-04-06: 6_365
-  2020-04-06: 6_475
-  2021-04-06: 6_515
+  2015-04-06:
+    value: 5_965
+    metadata:
+      reference:
+        - title: National Insurance Contributions Act 2015 Sch 1 para 3 (substituting s 11(4) of the Social Security Contributions and Benefits Act 1992)
+          href: https://www.legislation.gov.uk/ukpga/2015/5/schedule/1/paragraph/3/enacted
+        - title: Social Security Contributions and Benefits Act 1992 s 11(4) (as at 6 April 2016, unchanged for 2016-17)
+          href: https://www.legislation.gov.uk/ukpga/1992/4/section/11/2016-04-06
+  2017-04-06:
+    value: 6_025
+    metadata:
+      reference:
+        - title: The Social Security (Contributions) (Rates, Limits and Thresholds Amendments and National Insurance Funds Payments) Regulations 2017 reg 3(b)
+          href: https://www.legislation.gov.uk/uksi/2017/415/regulation/3/made
+  2018-04-06:
+    value: 6_205
+    metadata:
+      reference:
+        - title: The Social Security (Contributions) (Rates, Limits and Thresholds Amendments and National Insurance Funds Payments) Regulations 2018 reg 3(b)
+          href: https://www.legislation.gov.uk/uksi/2018/337/regulation/3/made
+  2019-04-06:
+    value: 6_365
+    metadata:
+      reference:
+        - title: The Social Security (Contributions) (Rates, Limits and Thresholds Amendments and National Insurance Funds Payments) Regulations 2019 reg 3(b)
+          href: https://www.legislation.gov.uk/uksi/2019/262/regulation/3/made
+  2020-04-06:
+    value: 6_475
+    metadata:
+      reference:
+        - title: The Social Security (Contributions) (Rates, Limits and Thresholds Amendments and National Insurance Funds Payments) Regulations 2020 reg 3(b)
+          href: https://www.legislation.gov.uk/uksi/2020/299/regulation/3/made
+  2021-04-06:
+    value: 6_515
+    metadata:
+      reference:
+        - title: The Social Security (Contributions) (Rates, Limits and Thresholds Amendments and National Insurance Funds Payments) Regulations 2021 reg 3
+          href: https://www.legislation.gov.uk/uksi/2021/157/regulation/3/made
   2022-04-06:
     value: 6_725
     metadata:
       reference:
-        - title: The Social Security (Contributions) (Rates, Limits and Thresholds Amendments and National Insurance Funds Payments) Regulations 2022(3)(b)
-          href: https://www.legislation.gov.uk/uksi/2022/232/regulation/3/made#regulation-3-b
+        - title: The Social Security (Contributions) (Rates, Limits and Thresholds Amendments and National Insurance Funds Payments) Regulations 2022 reg 3(b)
+          href: https://www.legislation.gov.uk/uksi/2022/232/regulation/3/made
+  2023-04-06:
+    value: 6_725
+    metadata:
+      reference:
+        - title: Social Security Contributions and Benefits Act 1992 s 11(4)(b) (as at 6 April 2023)
+          href: https://www.legislation.gov.uk/ukpga/1992/4/section/11/2023-04-06
+  2024-04-06:
+    value: 6_725
+    metadata:
+      reference:
+        - title: Social Security Contributions and Benefits Act 1992 s 11(4)(b) (as at 6 April 2024)
+          href: https://www.legislation.gov.uk/ukpga/1992/4/section/11/2024-04-06
   2025-04-06:
     value: 6_845
     metadata:
       reference:
-        - title: "GOV.UK | Rates and allowances: National Insurance contributions"
-          href: https://www.gov.uk/government/publications/rates-and-allowances-national-insurance-contributions/rates-and-allowances-national-insurance-contributions
+        - title: The Social Security (Contributions) (Rates, Limits and Thresholds Amendments, National Insurance Funds Payments and Extension of Veteran's Relief) Regulations 2025 reg 3(a)
+          href: https://www.legislation.gov.uk/uksi/2025/288/regulation/3/made
   2026-04-06:
     value: 7_105
     metadata:
       reference:
-        - title: "GOV.UK | Rates and allowances: National Insurance contributions"
-          href: https://www.gov.uk/government/publications/rates-and-allowances-national-insurance-contributions/rates-and-allowances-national-insurance-contributions
+        - title: The Social Security (Contributions) (Rates, Limits and Thresholds Amendments, National Insurance Funds Payments and Extension of Veteran's Relief) Regulations 2026 reg 3(a)
+          href: https://www.legislation.gov.uk/uksi/2026/231/regulation/3/made
 metadata:
   unit: currency-GBP
+  period: year
   label: NI class 2 small profits threshold
-  uprating:
-    parameter: gov.economic_assumptions.indices.obr.consumer_price_index
-    start_instant: 2022-04-06
+  uprating: gov.economic_assumptions.indices.obr.consumer_price_index
   reference:
-    - https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/882271/Table-a4.pdf
-    - https://www.gov.uk/government/publications/rates-and-allowances-national-insurance-contributions/rates-and-allowances-national-insurance-contributions
+    - title: Social Security Contributions and Benefits Act 1992 s 11
+      href: https://www.legislation.gov.uk/ukpga/1992/4/section/11
+    - title: "GOV.UK | Rates and allowances: National Insurance contributions"
+      href: https://www.gov.uk/government/publications/rates-and-allowances-national-insurance-contributions/rates-and-allowances-national-insurance-contributions
diff --git a/policyengine_uk/parameters/gov/hmrc/national_insurance/class_4/rates/additional.yaml b/policyengine_uk/parameters/gov/hmrc/national_insurance/class_4/rates/additional.yaml
@@ -1,19 +1,33 @@
 description: The additional National Insurance rate paid above the Upper Profits Limit for self-employed profits.
 values:
-  2015-04-01: 0.02
-  2022-04-01:
-    value: 0.035
+  2015-04-06:
+    value: 0.02
+    metadata:
+      reference:
+        - title: National Insurance Contributions Act 2011 s 2(1)(b) (additional Class 4 percentage of 2% from 6 April 2011)
+          href: https://www.legislation.gov.uk/ukpga/2011/3/section/2/enacted
+        - title: Social Security Contributions and Benefits Act 1992 s 15(3ZA)(b) (as at 6 April 2015)
+          href: https://www.legislation.gov.uk/ukpga/1992/4/section/15/2015-04-06
+  # Class 4 is charged on the year's profits, so 2022-23 has one rate for the
+  # whole tax year. The Health and Social Care Levy (Repeal) Act 2022 replaced
+  # the 3.25% that the Health and Social Care Levy Act 2021 s 5(2) had set.
+  2022-04-06:
+    value: 0.0273
     metadata:
       reference:
-        - title: Autumn Budget and Spending Review 2022
-          href: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1043689/Budget_AB2021_Web_Accessible.pdf
-  2024-01-01:
+        - title: Health and Social Care Levy (Repeal) Act 2022 s 2(2)(b) (additional Class 4 percentage of 2.73% for the tax year 2022-23)
+          href: https://www.legislation.gov.uk/ukpga/2022/43/section/2
+  2023-04-06:
     value: 0.02
     metadata:
       reference:
-        - title: National Insurance Contributions (Reduction in Rates) Act 2024 s 1
-          href: https://www.legislation.gov.uk/ukpga/2024/5/section/1
+        - title: Social Security Contributions and Benefits Act 1992 s 15(3ZA)(b) (as at 6 April 2023)
+          href: https://www.legislation.gov.uk/ukpga/1992/4/section/15/2023-04-06
 metadata:
   label: NI class 4 additional rate
   unit: /1
-  reference: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/882271/Table-a4.pdf
+  reference:
+    - title: Social Security Contributions and Benefits Act 1992 s 15(3ZA)
+      href: https://www.legislation.gov.uk/ukpga/1992/4/section/15
+    - title: "GOV.UK | Rates and allowances: National Insurance contributions"
+      href: https://www.gov.uk/government/publications/rates-and-allowances-national-insurance-contributions/rates-and-allowances-national-insurance-contributions
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		- Fix Class 2 National Insurance for 2015-16 to 2023-24 against s.11 SSCBA 1992: charge £3.45 a week in 2023-24; from 2022-23 charge only profits above the Class 2 lower profits threshold (£11,908, then £12,570), with profits from the small profits threshold up to it treated as paid; keep the small profits threshold at £6,725 in 2023-24 and 2024-25 and correct it to £5,965 in 2015-16 and 2016-17; date the abolition 6 April 2024. Class 2 now tests its thresholds on the profits Class 4 is charged on (s.11(3)), after capital allowances, the trading allowance and loss relief, not on self-employment income. A full year of Class 2 is every contribution week in it, so 53 weeks in 2019-20. The Universal Credit minimum income floor's notional Class 2 follows the same rule, so it deducts no Class 2 in 2022-23 and 2023-24 on a threshold the lower profits threshold covers. Every value now cites its amending instrument.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		- Fixed Class 4 NICs against s.15 SSCBA 1992: the 2023-24 lower profits limit is £12,570 (it was £11,908), the 2022-23 rates are 9.73% and 2.73% for the whole year (they were 10.25% and 3.5%), the 2023-24 additional rate is 2% (it was 3.5%), and the 2015-16 upper profits limit is £42,385. Every Class 4 limit and rate from 2015-16 to 2025-26 now cites its legal source.