Form

Council Tax Base (CTB): Validation checks

Updated 25 September 2026

Applies to England

Please read this guidance before submitting the CTB form.

The CTB Form contains validation checks designed to identify possible errors, inconsistencies and significant changes from the previous year. These include checks against data reported elsewhere in the form and against data reported in the 2025 CTB Form using validation parameters set by the Ministry of Housing, Communities and Local Government (MHCLG).

The CTB workbook contains two types of checks:

1. error messages shown in red within the CTB Form and supporting tabs, and
2. validation checks shown on the Validation tab.

Further information on these checks and the action required is provided below.

Once the form has been completed, check that there are no unresolved error messages and that comments have been provided for all validation queries requiring an explanation. Authorities submitting forms with unresolved errors or missing required validation comments will be asked to correct and resubmit the form.

Council tax bands

Unless otherwise stated, the validation checks described below are applied to the total across all council tax bands rather than to each band individually. Authorities should nevertheless check that figures have been entered in the correct bands.

Arithmetic calculations

Before submitting the form, please ensure that all calculations are correct and that data has been entered to the required number of decimal places. All arithmetic calculations have been built into the form. Cells containing calculations have a green background and a green border and should not be amended. The calculations are as follows:

Part 1

• Line 4: Number of chargeable dwellings on 5 October 2026

  Line 4 = line 1 – line 2 – line 3

• Line 6: Number of dwellings effectively subject to council tax for the band by virtue of disabled relief

  Line 6 = line 5 moved to the next lower council tax band

• Line 7: Number of chargeable dwellings adjusted in accordance with lines 5 and 6

  Line 7 = line 4 – line 5 + line 6 (or in the case of column 1, line 6)

• Line 11: Number of dwellings in line 7 classed as second homes on 5 October 2026

  Line 11 = line 11a + line 11b + line 11c

• Line 15: Total number of dwellings in line 7 classed as empty on 5 October 2026

  Line 15 = line 12 + line 13 + line 14

• Line 18: Number of dwellings empty for more than 6 months after excluding properties empty due to flooding and those that previously would have received a Class A exemption

  Line 18 = line 16 – line 16a – line 17

• Line 19: Number of dwellings in line 7 where there is a liability to pay 100% council tax before the Family Annexe discount is applied

  Line 19 = line 7 – line 20

• Line 20: Number of dwellings in line 7 that are assumed to be subject to a discount or a premium before the Family Annexe discount is applied

  Line 20 = line 8 + line 9 + line 10 + line 11b + line 11c + line 13 + line 14

• Line 22: Number of dwelling equivalents after applying discounts (including the family annexe discount) and premiums to calculate the tax base

  Line 22 (to 2 decimal places) = line 7 – (line 8 x 0.25) – (line 9 x 0.25) – (line 10 x 0.5) – ‘Second Homes’ tab row 84 (total reductions in dwelling equivalent after empty and second homes discounts and premiums are applied) – line 21

• Line 24: Total number of band D equivalents

  Line 24 (to 2 decimal places) = line 22 x line 23

• Line 26: Tax base

  Line 26 (to 2 decimal places) = line 24 column 10 + line 25

Part 2

• Line 29: Number of dwelling equivalents after applying discounts, premiums, and local council tax support

  Line 29 (to 2 decimal places) = line 27 – line 28

• Line 31: Total number of band D equivalents after allowance for council tax support

  Line 31 (to 2 decimal places) = line 29 x line 30

• Line 33: Tax base after allowance for council tax support

  Line 33 (to 2 decimal places) = line 31 column 10 + line 32

Error messages

The CTB workbook contains automated error checks within the CTB Form, CTB Supplementary Form, CT Support, Family Annexe, Empty Properties and Second Homes tabs.

These checks are designed to identify:

• inconsistencies between related figures within the form;
• inconsistencies between figures reported on different tabs;
• formulas or automatically populated figures that have been overwritten; and
• missing or invalid information, including required dropdown selections.

Error messages are displayed in red. Where an error message is displayed, the issue must be reviewed and corrected so that the error message disappears before the form is submitted. These error messages do not require a comment on the Validation tab.

Specific validation checks on the Validation tab

The Validation tab contains checks on figures reported in the CTB workbook. Column N shows the outcome of each check:

• ‘OK’ means that no comment is required.
• ‘Please comment’ means that the figures should be reviewed and a clear and sufficiently detailed explanation provided in Column P.

A validation flag does not necessarily mean that the figure reported is incorrect. Where the figure is correct, the comment should explain the reason for the value or change identified by the check.

Where comments are required on the Validation tab, explanations such as “OK”, “This is how it is”, “It has changed” or “Don’t know” are not sufficient. A useful explanation should identify what has changed, why it has changed and, where possible, the effect on the figures reported.

Main form checks

Test 1: CTB form Line 1 against the total number of dwellings on the Valuation List

The figure reported in CTB Form Line 1 should be exactly the same as the data provided by the Valuation Office Agency as at 9 September 2026. Any difference identified by Test 1 should be investigated with the Local Valuation Office. Where a revised figure is confirmed, please provide a copy of the confirmation email from the Local Valuation Office when submitting the form.

Year on year comparisons

The table below sets out the validation checks applied to the main CTB Form and the thresholds at which an explanation is required. Unless otherwise stated, comparisons are made against data reported in the 2025 CTB Form. Test 16 is compared against the 2026-27 CTR1 form.

Test	Description	Threshold requiring an explanation
2	Total number of dwellings in Line 1	Increase of more than 1,000 dwellings AND more than 1.5%; OR any decrease compared with the previous year
3	Total number of exempt dwellings	Change of more than 150 dwellings AND more than 10% compared with the previous year
4	Demolished dwellings and dwellings outside the authority area, Line 3	Change of more than 20 dwellings compared with the previous year
5	Dwellings subject to a disability reduction, Line 5	Increase of more than 20 dwellings AND more than 10%; OR decrease of more than 20 dwellings AND more than 5%
6	Single adult household 25% discounts, Line 8	Change of more than 750 dwellings AND more than 2% compared with the previous year
7	25% discounts where all but one resident is disregarded, Line 9	Change of more than 100 dwellings AND more than 10% compared with the previous year
8	50% discounts where all residents are disregarded, Line 10	Change of more than 30 dwellings AND more than 10% compared with the previous year
9	Second homes, Line 11	Change of more than 100 dwellings AND more than 10% compared with the previous year
10	Empty dwellings receiving a 0% discount, Line 12	Change of more than 100 dwellings AND more than 25% compared with the previous year
11	Empty dwellings receiving a discount, Line 13	Change of more than 100 dwellings AND more than 25% compared with the previous year
12	Empty dwellings charged the Empty Homes Premium, Line 14	Change of more than 50 dwellings AND more than 20% compared with the previous year
13	Total number of empty dwellings, Line 15	Change of more than 100 dwellings AND more than 20% compared with the previous year
14	Long-term empty dwellings, Line 18	Change of more than 200 dwellings AND more than 20% compared with the previous year
15	Dwellings subject to Class O exemption, Line 25	Change of more than 20 dwellings compared with the previous year
16	Tax base after council tax support, Line 31	Change of more than 1,000 dwellings AND more than 2% compared with the tax base after council tax support reported in Line 7 of the 2026-27 CTR1 form in March 2026
17	Reduction in tax base as a result of local council tax support, Line 28	Change of more than 250 dwellings AND more than 5% compared with the previous year
18	Family Annexe discount reduction, Line 21	Change of more than 4 dwellings compared with the previous year

Supplementary form checks

The table below sets out the validation checks applied to the CTB Supplementary Form and the thresholds at which an explanation is required. Comparisons are made against data reported in the 2025 CTB Supplementary Form.

Test	Description	Threshold requiring an explanation
19	Class F exemptions (dwellings left empty by deceased persons) on 5 October 2026	Change of more than 75 dwellings AND more than 10% compared with the previous year
20	Class M and Class N exemptions (student exemptions) on 5 October 2026	Increase of more than 100 dwellings AND more than 7.5%; OR decrease of more than 100 dwellings AND more than 10% compared with the previous year
21	Class U exemptions (dwellings occupied only by a person or persons who are severely mentally impaired) on 5 October 2026	Increase of more than 25 dwellings AND more than 10%; OR decrease of more than 25 dwellings AND more than 5% compared with the previous year

Consistency checks

Tests 22 to 24 identify inconsistencies between related figures. Where one of these checks is flagged, the figures should be reviewed and any inconsistency corrected. A comment should also be provided in Column P where Column N shows ‘Please comment’.

Test 22: Reduction in tax base due to Family Annexe discount on 5 October 2026

Line A on the Family Annexe tab cannot exceed 50% of the corresponding number of dwellings reported in Line B.

Test 23: Total number of exemptions

The total number of exemptions reported in Part 1 of the CTB Supplementary Form must equal Line 2 of the main CTB Form.

Test 24: Total Class M and N exemptions

The Class M and Class N figures reported in the second question of Part 3 must equal the corresponding Class M and Class N figures reported in Part 1 of the CTB Supplementary Form.

Test 25: The number of exempt dwellings as a percentage of the total stock

An explanation is required where the total number of exemptions reported in Line 2 exceeds 4% of the total dwelling stock reported in Line 1. This validation is not a comparison with the previous year.

Contact detail checks

Tests 26 and 27 will flag if contact details have not been provided on the ‘CTB Form’ tab.

These details are required so that MHCLG can contact the appropriate person if an issue with the form needs to be resolved. The certifier’s email address is also required to help us confirm that certification has been provided by the appropriate person.

Further comments

Space has been provided in row 75 of the ‘Validation’ tab to provide any further comments relating to the data provided in the CTB form.

Ministry of Housing, Communities & Local Government

September 2026