tax-calendar

---
name: tax-calendar
description: Turns your business's own reference dates, its accounting year end or incorporation date, its VAT quarter stagger, whether it runs payroll, and whether Making Tax Digital for Income Tax applies, into a single calendar of every deadline that actually falls due in the next 12 months, each one dated, sourced to the gov.uk or Companies House page that sets it, and carrying the penalty for missing it. Use when you want every filing and payment date in one place instead of piecing it together from separate VAT, payroll, Self Assessment and Companies House reminders, or when you have just taken on a new accounting year and need next year's dates worked out from this year's.
---

# Every deadline that falls due in your next 12 months, on one page, dated from your own business, not a generic list

You give this whether the business is a limited company or a sole trader or partnership, its year end or incorporation date, its VAT registration date and quarter stagger if VAT registered, whether it runs payroll and for how many employees, and whether its Self Assessment income puts it inside Making Tax Digital for Income Tax. You get back a single calendar, in date order, of every deadline that actually applies to this business in the coming year, each one calculated from the business's own dates rather than copied from a generic list, with the gov.uk or Companies House rule behind it and what happens if it is missed. It will not include a deadline for a relief, a scheme or a filing the business is not actually in. A calendar padded with irrelevant dates is as unsafe as one missing a real one, because the owner stops reading it.

## What it does

1. **Fix the business's own reference dates before calculating anything.** For a limited company, record the date of incorporation and the accounting reference date, which sets the financial year end; both are held by Companies House and can be checked on the company's own page there. For a sole trader or partnership, there is no equivalent choice: the tax year for Self Assessment is fixed at 6 April to 5 April regardless of when the business started trading. Record the VAT registration date and the quarter stagger group if VAT registered, since a business staggered to March, June, September and December has different VAT dates from one staggered to January, April, July and October. Record whether the business runs payroll and the number of employees, and whether the owner's Self Assessment income for the tax year is expected to be over the Making Tax Digital for Income Tax threshold. Every date calculated after this step depends on getting these reference facts right first.

2. **If the business is a company, calculate the four Companies House and Corporation Tax deadlines from the accounting reference date.** GOV.UK states these as a single table: file first accounts with Companies House "21 months after the date you registered with Companies House", file annual accounts with Companies House "9 months after your company's financial year ends", pay Corporation Tax "9 months and 1 day after your 'accounting period' for Corporation Tax ends", and file a Company Tax Return "12 months after your accounting period for Corporation Tax ends." A company's accounting period for Corporation Tax is normally the same 12 months as its financial year, so all four dates run from the same year end once the business is past its first year.

3. **Calculate the confirmation statement date from the incorporation anniversary, and repeat it every year.** This is a Companies House filing, separate from the annual accounts, and it is easy to miss precisely because it repeats on a moving date rather than a fixed calendar day. The review period runs for 12 months from either the incorporation date, for the first statement, or the date on the previous confirmation statement after that, and the filing itself is due "up to 14 days after the review period has ended." Missing it carries a real consequence stated plainly: "You can be fined up to GBP 5,000 and your company may be struck off if you do not file your confirmation statement."

4. **If the business is a sole trader or partnership, fix the Self Assessment dates for the tax year just ended, and flag the 5 October registration deadline as the most time sensitive.** A business new to Self Assessment, or one that did not need to file for the previous tax year, "must tell HMRC by 5 October if you need to complete a tax return for the previous year." After that, the paper return is due 31 October, the online return and the balancing payment are both due 31 January, and a second payment on account, where the previous year's tax bill triggered one, is due 31 July. These four dates repeat every year on the same calendar days regardless of when in the year the business actually trades most of its turnover, which is why a seasonal hospitality business with its busiest months over Christmas still owes its balancing payment in the quiet weeks of January.

5. **If VAT registered, calculate every quarterly return and payment date in the coming 12 months from the stagger group.** The rule is fixed and short: "the deadline for submitting your return online is usually one calendar month and 7 days after the end of an accounting period. This is also the deadline for paying HMRC." Apply this to each of the four quarters in the stagger group to produce four dates across the year, not one, and note that the payment deadline is when the money must actually reach HMRC, which means a payment method needing several working days to clear must be started ahead of the date itself.

6. **If the business is inside Making Tax Digital for Income Tax, calculate the four quarterly update deadlines and the Final Declaration date.** Using standard, non calendar, update periods, the four quarters run 6 April to 5 July, 6 July to 5 October, 6 October to 5 January and 6 January to 5 April, each due one calendar month after its own end, giving deadlines of 7 August, 7 November, 7 February and 7 May. The Final Declaration, which replaces the old Self Assessment return for anyone inside MTD for Income Tax, is due by the same 31 January used in step 4. Record the current penalty position exactly as stated, because it is genuinely softer this year than the ordinary rule: HMRC "will not apply penalty points for late quarterly updates during the 2026 to 2027 tax year", though "penalty points will still apply for late tax returns", so the quarterly updates themselves carry no point this year while the year end return still does.

7. **If the business runs payroll, calculate the repeating cycle and the four fixed year end dates.** The repeating obligation is the on-or-before rule for the Full Payment Submission, sent on or before each payday, with the payment itself due "by the 22nd of the month (or the 19th if paying by post)." The fixed dates that fall once a year regardless of pay frequency are: give employees their P60 "by 31 May"; report expenses and benefits and the Class 1A National Insurance owed by "6 July"; and pay that Class 1A National Insurance by "22 July (19 July if paying by cheque)." Put the repeating monthly obligation and the three fixed year end dates on the same calendar rather than two separate lists, since a missed year end date is usually missed because the owner was only tracking the monthly cycle.

8. **If the business owns or leases premises with a rateable value, record the local instalment dates as a flagged item rather than a calculated one.** Business rates instalments are set by the local billing authority on the actual bill, not by a single national rule, and typically run monthly from April, but the exact number of instalments and the start date vary by council and by whether a payment plan was agreed. Record this as an item to confirm against the current year's bill rather than calculating a date this skill cannot verify nationally, and note the annual point at which reliefs such as Small Business Rate Relief or Retail, Hospitality and Leisure relief need re-checking for the new rates year, which the business-rates skill in this pack works through in full.

9. **Assemble every date from steps 2 to 8 into one calendar in date order, covering the 12 months from today.** Merge the company, VAT, Self Assessment, MTD and payroll dates into a single chronological list rather than separate sections by tax type, because a September page listing dates by type hides the fact that a VAT payment and a payroll payment fall in the same week. Every entry carries the deadline date, what is due, the source page, and the stated consequence of missing it.

10. **Hand the finished reference dates to Codex and let it calculate and sequence the calendar.** Claude hands over the business's reference dates, which tax regimes apply to it, and the exact rule text and source for every deadline type from steps 2 to 8. Codex makes no judgement about which regimes apply: it calculates the specific dates from the reference dates it is given and sequences them. Run it from the folder holding the business's own records:

    ```
    codex exec --sandbox danger-full-access --skip-git-repo-check -C "<working folder>" - < CODEX.md
    ```

    What comes back is the single sequenced calendar, a by-regime breakdown for checking the calculation, the evidence register naming the source of every rule applied, and gaps.md, plus the counts you check in the next section.

## Then it checks

1. Every regime the business is actually in, company filings, VAT, Self Assessment or MTD for Income Tax, payroll, and business rates, has at least one entry on the calendar, and no regime the business is not in appears on it.
2. Every date on the calendar is calculated from the business's own reference date supplied in step 1, and no date is copied from a generic example without that calculation shown.
3. The four company deadlines in step 2, where the business is a company, are checked against each other and none precedes an earlier one that it logically depends on, for example the Company Tax Return filing date is never shown earlier than the Corporation Tax payment date it follows.
4. The confirmation statement date is shown as a repeating annual entry tied to the review period, not a single one-off date.
5. Where MTD for Income Tax applies, all four quarterly update deadlines and the Final Declaration date appear, and the current penalty position for late quarterly updates in the 2026 to 2027 tax year is stated accurately rather than assumed to match the ordinary points rule.
6. Every entry on the calendar names its source page and the stated consequence of missing it, and no entry is present with an empty source field.

Any check fails: name it, redo that step once. Failed twice: say what is wrong and stop.

## Rules
- Public information only.
- Never invent a fact, a number or a quote.
- Anything sent in someone's name says whose name it is.
- Never state a typical number of deadlines, a typical penalty cost, or how much time a business like this one usually spends on compliance in a year. No published figure exists for a single independent UK hospitality business, and the only number that matters to this owner is the count of dates on their own calendar.
- Never calculate a deadline for a regime the business has not confirmed it is in. A VAT date is calculated only where a VAT registration date is supplied, an MTD date only where the owner has confirmed the income threshold is met, and a payroll date only where a PAYE scheme is confirmed running.
- Never predict a rate, a threshold or a penalty rule that has not yet been announced for a future year. Where this year's rule is known and next year's has not been published, the calendar states this year's rule and marks next year as not yet announced rather than assuming it continues unchanged.
- Never treat the business rates instalment dates as calculated. They are set locally and are recorded as a flagged item to confirm against the current bill, never as a computed date.
- This output is a working document prepared for the owner's own accountant or tax adviser to check before it is relied on. It applies published deadlines and published penalty rules to the business's own supplied dates. It is not tax advice, and it does not replace the reminder services HMRC and Companies House can send directly to the business.

## Built from
- HM Revenue and Customs and GOV.UK, "Self Assessment tax returns: Deadlines", https://www.gov.uk/self-assessment-tax-returns/deadlines, read 23 September 2026: the 5 October registration deadline, the 31 October paper deadline, the 31 January online and payment deadline, and the 31 July payment on account deadline, in step 4.
- GOV.UK, "Prepare annual accounts for a private limited company", https://www.gov.uk/prepare-file-annual-accounts-for-limited-company, no date shown on the page, read 23 September 2026: the first accounts, annual accounts, Corporation Tax payment and Company Tax Return filing deadlines table in step 2.
- Companies House and GOV.UK, "Filing your company's confirmation statement", https://www.gov.uk/guidance/filing-your-companys-confirmation-statement, read 23 September 2026: the 12 month review period, the 14 day filing window, and the GBP 5,000 fine and strike off risk, in step 3.
- HM Revenue and Customs and GOV.UK, "Submit your VAT Return", https://www.gov.uk/submit-vat-return, read 23 September 2026: the one calendar month and 7 days filing and payment deadline in step 5.
- HM Revenue and Customs and GOV.UK, "Use Making Tax Digital for Income Tax: Send quarterly updates", https://www.gov.uk/guidance/use-making-tax-digital-for-income-tax/send-quarterly-updates, read 23 September 2026: the four standard quarterly update deadlines and the current 2026 to 2027 penalty point position for late quarterly updates, in step 6.
- HM Revenue and Customs and GOV.UK, "Running payroll: Paying HMRC", https://www.gov.uk/running-payroll/paying-hmrc, read 23 September 2026: the 22nd electronic and 19th postal payment deadline in step 7.
- HM Revenue and Customs and GOV.UK, "Get your employee's P60 form", https://www.gov.uk/paye-forms-p45-p60-p11d/p60, read 23 September 2026: the 31 May P60 deadline in step 7.
- HM Revenue and Customs and GOV.UK, "Expenses and benefits for employers: Deadlines", https://www.gov.uk/employer-reporting-expenses-benefits/deadlines, read 23 September 2026: the 6 July reporting deadline and the 22 July or 19 July Class 1A National Insurance payment deadline in step 7.

# tax-calendar

## You are given
The business's own reference dates: whether it is a limited company or a sole trader or partnership, its date of incorporation and accounting reference date if a company, its VAT registration date and quarter stagger group if VAT registered, whether it runs payroll and how many employees, whether its Self Assessment income is confirmed by the owner to be inside Making Tax Digital for Income Tax for the current tax year, and whether it owns or leases premises with a business rates bill. For every deadline type that applies to this business, the exact rule Claude has already read from the source page: the number of months or days the deadline falls after a stated reference point, the fixed calendar date where one applies, and the stated consequence of missing it. Today's date, for calculating the coming 12 month window. All judgement calls, including which regimes the business is actually in and which deadline rules apply to it, have already been made and are supplied to you.

## Produce
Write into a `./tax-calendar-output/` folder:

1. `calendar.csv` with these columns in this order: `deadline_date`, `regime`, `what_is_due`, `reference_date_it_was_calculated_from`, `calculation_rule`, `source_page`, `consequence_of_missing_it`. `regime` is exactly one of `Companies House`, `Corporation Tax`, `Self Assessment`, `Making Tax Digital for Income Tax`, `VAT`, `PAYE`, `business rates`. Rows are sorted by `deadline_date` ascending. Only dates falling within the 12 months from today, as supplied, appear in this file.
2. `regime-breakdown.csv` with columns: `regime`, `applies_to_this_business`, `reference_date_supplied`, `deadline_type`, `calculated_deadline_date`, `calculation_shown`. One row per deadline type within each regime the business is in, showing the arithmetic from the reference date to the calculated date, for example an accounting reference date of 31 December plus 9 months giving 30 September. `applies_to_this_business` is `yes` or `no`; a regime marked `no` has no rows in `calendar.csv`.
3. `evidence-register.csv` with columns: `regime`, `deadline_type`, `rule_text_verbatim`, `source_page`, `date_read`. One row per rule used to calculate a deadline, quoting the exact rule text supplied.
4. `gaps.md` a numbered list of: every regime with no reference date supplied where one was needed to calculate a deadline; every deadline type flagged as locally set rather than calculated, specifically business rates instalment dates; any rule supplied without a source page or a read date; and any deadline that could not be calculated because the reference date supplied was incomplete or contradictory.

## Rules
- Codex calculates and sequences only. It never decides which regimes the business is in, never estimates a reference date that was not supplied, and never predicts a future rate, threshold or deadline rule that has not been confirmed.
- A regime with no reference date supplied produces no calculated deadline. It is recorded in `gaps.md`, never estimated from a typical business's dates.
- Business rates instalment dates are never calculated. Every business rates entry in `calendar.csv` is a flagged reminder to confirm against the current year's bill, with `calculation_rule` reading exactly `set locally, confirm against current bill, not calculated`.
- Never carry a deadline rule forward from a previous tax year without it being separately supplied as current for this year. Where a rule for next year has not yet been announced, no row is written for it and it is recorded in `gaps.md` instead.
- Never write a typical number of deadlines, a typical penalty cost or any industry benchmark into any file.
- Use British English, GBP written as `GBP` or the pound sign, and DD Month YYYY dates. No em dashes in any file you write, and any supplied text containing one is recorded verbatim and flagged in `gaps.md`.
- Every quoted rule text is copied exactly, including its punctuation and capitalisation.
- Every file ends with this line: this is a working document prepared for the owner's own accountant or tax adviser to check before it is relied on. It applies supplied deadline rules to the business's own supplied dates and does not replace HMRC's or Companies House's own reminder services.

## Return
The absolute path of every file written, the row count of `calendar.csv`, the count of deadlines by regime, the earliest and latest deadline date on the calendar, the count of regimes marked as not applying to this business, the count of flagged rather than calculated entries, and the `gaps.md` item count.