UK companies and crypto: the 10-day window versus 'previous nine days'
Statute says 'within a period of 10 days'; HMRC says 'previous nine days'. How they relate, and how to document your convention.
Our earlier pooling explainer noted that companies match disposals backward, not forward. Readers asked why the statute speaks of a 10-day period while HMRC's crypto manual speaks of nine days. This follow-up sets out both texts and what systems should record.
The two texts
For corporation tax, TCGA 1992 s.107(3) applies where securities are acquired and later disposed of "within a period of 10 days" [1]. Fungible assets dealt in without identifying particular units fall within the s.104 definition of securities [6], and HMRC applies these company rules to tokens [2].
HMRC's Cryptoassets Manual describes the same rule as matching a disposal made within ten days of an acquisition with acquisitions in the previous nine days, first in first out, ahead of the pool [2]. HMRC's Capital Gains Manual for shares uses the same pairing of wording and also cites s.107(3) [3]. So HMRC itself uses both phrases side by side; it does not present them as different rules.
How the two descriptions fit
One reading reconciles them: the 10-day period counts the disposal day plus the nine days before it. Same-day acquisitions are handled first by s.105, which s.107(3) expressly preserves [1][4]. The nine prior days are then the s.107 window.
- 15 March: same-day acquisitions matched first (s.105)
- 6 to 14 March: acquisitions matched next, earliest first (s.107)
- 5 March and earlier: not matched by s.107; disposal falls to the s.104 pool
- Pool is used only for any quantity left over
The uncertain case is an acquisition exactly 10 days before the disposal, here 5 March. Neither the statute nor the manuals we read states an explicit counting convention, and HMRC's worked examples use gaps of five and six days, which fall inside any reading [2][3][7]. Treating 5 March as outside matches HMRC's previous nine days wording, but we could not find guidance that settles the point.
HMRC's crypto example is clear-cut: a company buys 500 tokens on 30 August and sells 4,000 on 4 September. The 500 are matched first and the other 3,500 come from the pool at average cost [2].
What does not apply to companies
The 30-day forward rule for individuals is in s.106A, which has effect for capital gains tax but not corporation tax [5]. A company disposal is therefore not reopened by a purchase made after it, and its matching can be settled on the disposal date. If more tokens are acquired in the window than are sold, the excess joins the s.104 pool; if more are sold, the excess is matched to the pool [1].
What to do
- Write down the window your system uses, for example disposal day plus nine prior calendar days, and the time zone used to assign dates.
- Run same-day matching before the prior-days window, and earliest acquisition first within it [1][2].
- Flag any acquisition exactly 10 days before a disposal for manual review rather than silently including or excluding it.
- Never apply the individual 30-day forward rule to a company [5].
- Get your adviser to sign off the convention in writing and keep that with your tax workpapers.
Sources
- Taxation of Chargeable Gains Act 1992, section 107 (legislation.gov.uk)
- CRYPTO41350 - Cryptoassets for businesses: Corporation Tax: Corporation Tax on Chargeable Gains - pooling (HM Revenue & Customs)
- CG51615 - Share identification rules for corporation tax: the 10 day rule: general (HM Revenue & Customs)
- Taxation of Chargeable Gains Act 1992, section 105 (legislation.gov.uk)
- Taxation of Chargeable Gains Act 1992, section 106A (legislation.gov.uk)
- Taxation of Chargeable Gains Act 1992, section 104 (legislation.gov.uk)
- CG51616 - Share identification rules: the 10 day rule: examples (HM Revenue & Customs)
General information for finance teams, current as of publication. Not legal, tax or accounting advice.