CryptoLens/Case studies

UK crypto tax case studies

Four illustrative scenarios showing how the HMRC matching rules actually change the tax bill — Section 104 pooling, the 30-day bed-and-breakfast rule, and same-day matching. Every number is calculated with the same constants the live engine uses.

These are illustrative scenarios, not real customers. Actual results depend on your specific transactions. CryptoLens does not give tax advice — consult an accountant for your final return.

Illustrative scenario · Section 104 pool

The Casual Holder

Bought 1 BTC during the 2022 lows, picked up a second 1 BTC near the 2024 highs. Sold half a coin in November 2024 to fund a deposit.

Acquisitions
  • Jan 2022Buy 1 BTC for £15,000
  • Jul 2024Buy 1 BTC for £45,000
Disposals
  • 15 Nov 2024Sell 0.5 BTC for £30,000 (post-Oct rate)
Without UK-first tools (FIFO matching)
£4,680

Naive FIFO uses the first 1 BTC bought (£15,000) as cost. Half of that is £7,500 → £22,500 gain → £19,500 after £3k AEA → 24% higher-rate tax = £4,680.

With CryptoLens (Section 104 pool)
£2,880

Section 104 averages both buys to £30,000/BTC. Half a coin costs £15,000 → £15,000 gain → £12,000 after £3k AEA → 24% higher-rate tax = £2,880.

Saved £1,800 by applying Section 104 average-cost pooling correctly.
Show the math
  1. Section 104 pool after both buys: 2 BTC, total cost £60,000, average £30,000 per BTC.
  2. Disposal 0.5 BTC: proceeds £30,000, cost basis 0.5 × £30,000 = £15,000, gain £15,000.
  3. Tax year 2024/25 AEA = £3,000. Disposal is post-30-Oct so taxed at 18% basic / 24% higher.
  4. Taxable gain = £15,000 − £3,000 = £12,000.
  5. Higher-rate CGT = £12,000 × 24% = £2,880. (Basic-rate would be £12,000 × 18% = £2,160.)
  6. Naive FIFO comparison: 0.5 BTC of the £15,000 lot = £7,500 cost → £22,500 gain → (22,500 − 3,000) × 24% = £4,680.
Illustrative scenario · 30-day bed-and-breakfast

The DeFi Farmer

Holds ETH long-term, rotates in and out around yield opportunities. Sold 50 ETH on 1 July 2024 to redeploy, then re-entered the same position two weeks later.

Acquisitions
  • Mar 2024Buy 100 ETH for £180,000 (£1,800 each)
  • 15 Jul 2024Buy 50 ETH for £125,000 (£2,500 each)
Disposals
  • 1 Jul 2024Sell 50 ETH for £120,000 (pre-Oct rate)
Without UK-first tools (no B&B applied)
£5,400

Matched against the Section 104 pool only: cost basis 50 × £1,800 = £90,000, gain £30,000 → £27,000 after £3k AEA → 20% higher-rate tax = £5,400.

With CryptoLens (30-day B&B rule)
£0

The 30-day re-acquisition matches the disposal against the £125,000 re-buy. Proceeds £120,000 − cost £125,000 = £5,000 allowable loss, no tax this year, plus a £5,000 loss to carry forward.

Saved £5,400 in cash tax this year, plus a £5,000 carry-forward loss to offset future gains.
Show the math
  1. Disposal: 1 Jul 2024 sell 50 ETH for £120,000.
  2. Re-acquisition within 30 days: 15 Jul 2024 buy 50 ETH for £125,000.
  3. HMRC matching order: same-day → 30-day B&B → Section 104. The B&B rule matches the sell against the later buy of the same asset, so the £180k Section 104 pool is NOT touched.
  4. B&B disposal: proceeds £120,000, cost basis £125,000, allowable loss £5,000.
  5. Disposal pre-30-Oct, so CGT rates would be 10% / 20% — but the loss makes them academic.
  6. Naive comparison (no B&B): cost basis 50 × £1,800 = £90,000, gain £30,000, (30,000 − 3,000) × 20% = £5,400.
  7. Closing Section 104 pool stays at 100 ETH × £1,800 (the March acquisition is untouched).
Illustrative scenario · Section 104 pool (multi-year stacking)

The Whale

Bought ETH over three years at very different prices. Disposed of 15 ETH spread across the 2024/25 rate-change boundary.

Acquisitions
  • 2021Buy 10 ETH for £5,000 (£500 each)
  • 2022Buy 20 ETH for £24,000 (£1,200 each)
  • 2023Buy 20 ETH for £40,000 (£2,000 each)
Disposals
  • 15 Sep 2024Sell 8 ETH for £20,000 (pre-Oct rate)
  • 10 Dec 2024Sell 7 ETH for £19,600 (post-Oct rate)
Without UK-first tools (FIFO matching)
£5,504

FIFO uses the cheap 2021 batch first. First sale: cost £4,000, gain £16,000. Second sale: cost £7,000, gain £12,600. Applying AEA to higher-rate gains first: £9,600 × 24% + £16,000 × 20% = £5,504.

With CryptoLens (Section 104 pool)
£3,458

Section 104 averages all three buys to £1,380/ETH. First sale gain £8,960, second sale gain £9,940. Splitting the £3k AEA against post-Oct first, then taxing the rest: £6,940 × 24% + £8,960 × 20% = £3,458.

Saved £2,046 by applying Section 104 pooling across all three buys.
Show the math
  1. Section 104 pool: 50 ETH, total cost £5,000 + £24,000 + £40,000 = £69,000, average £1,380 per ETH.
  2. Disposal #1 (15 Sep, pre-Oct): proceeds £20,000, cost 8 × £1,380 = £11,040, gain £8,960.
  3. Disposal #2 (10 Dec, post-Oct): proceeds £19,600, cost 7 × £1,380 = £9,660, gain £9,940.
  4. Total gain £18,900. AEA £3,000 applied to higher-rate (post-Oct) first: £9,940 − £3,000 = £6,940 post-Oct, £8,960 pre-Oct.
  5. Higher-rate CGT: £6,940 × 24% + £8,960 × 20% = £1,665.60 + £1,792.00 = £3,457.60.
  6. Naive FIFO sells 8 ETH at £500 (cost £4,000, gain £16,000), then 2 ETH at £500 + 5 ETH at £1,200 (cost £7,000, gain £12,600). AEA placed similarly → £9,600 × 24% + £16,000 × 20% = £5,504.00.
Illustrative scenario · Same-day matching

The Active Trader

Long-term holder who also actively rotates positions. Bought and sold 5 BTC on the same day in August 2024 around an event.

Acquisitions
  • 2020-22Buy 10 BTC for £150,000 (£15,000 each)
  • 1 Aug 2024Buy 5 BTC for £200,000 (£40,000 each)
Disposals
  • 1 Aug 2024Sell 5 BTC for £210,000 (pre-Oct rate)
Without UK-first tools (Section 104 only)
£18,067

Without same-day matching, the buy enters the £150k pool first, dragging the average to about £23,333/BTC. Selling 5 BTC at £42,000 each shows a £93,333 gain. (£93,333 − £3,000) × 20% = £18,067.

With CryptoLens (same-day rule)
£1,400

The same-day rule matches the buy and sell directly: cost £200,000, proceeds £210,000, gain £10,000. The cheap 10 BTC pool is untouched. (£10,000 − £3,000) × 20% = £1,400.

Saved £16,667 this year by matching same-day buy-and-sell pairs first.
Show the math
  1. Pre-existing Section 104 pool: 10 BTC, total cost £150,000, average £15,000 per BTC.
  2. Same-day matching (HMRC priority rule #1): the 1 Aug buy of 5 BTC for £200,000 matches the 1 Aug sale of 5 BTC for £210,000 directly. Gain = £10,000.
  3. The pre-existing pool is unchanged: still 10 BTC × £15,000 average.
  4. Disposal pre-30-Oct: CGT rates 10% basic / 20% higher.
  5. Taxable gain = £10,000 − £3,000 AEA = £7,000. Higher-rate CGT = £7,000 × 20% = £1,400.
  6. Naive comparison (no same-day): buy enters the pool → 15 BTC, total cost £350,000, average ~£23,333. Sell 5 BTC: cost ~£116,667, proceeds £210,000, gain ~£93,333. (£93,333 − £3,000) × 20% ≈ £18,067.

These are illustrative scenarios, not real customers. Actual results depend on your specific transactions. CryptoLens does not give tax advice — consult an accountant for your final return.

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