Kept Some of the Sale Money? The Rollover Relief Rule That Taxes It First 2026/27

Rollover relief measures what you reinvest against your proceeds, not your gain. Hold back too much cash and the relief shrinks to nothing.

Zazentax Rollover Relief Series, Part 2 of 3 · Updated July 2026 · Reading time: about 5 minutes

Part 1 of this series showed the clean case: sell a business asset, reinvest everything, defer the whole gain. Real life is rarely that tidy. The new premises may cost less than the old ones fetched, or the owner may deliberately keep some cash aside for working capital. The relief survives partial reinvestment, but it applies a strict and frequently misunderstood test to decide how much of the gain can still be deferred.

The misunderstanding is almost always the same one. People assume they must reinvest the gain to defer it. In fact the law compares the cost of the new asset with the full sale proceeds of the old one, and every pound of proceeds not reinvested is treated as taxable gain first. Consequently, retaining even a modest slice of the money can expose a surprising share of the gain, and retaining too much extinguishes the relief altogether.

The Rule in One Sentence

The amount of gain that cannot be deferred equals the cash retained, meaning sale proceeds minus the amount reinvested, and only the remainder of the gain rolls over. Where disposal costs such as legal and agent fees are incurred on the sale, it is the net proceeds after those costs that must be reinvested, a small but helpful softening of the test.

Worked Example One: Keeping a Little

Marco sells his storage yard for £300,000. It cost him £190,000, so his gain is £110,000. The replacement site he buys costs £262,000, which means he has retained £300,000 minus £262,000, which equals £38,000 of cash. That £38,000 is immediately chargeable to Capital Gains Tax, the tax on profits from selling assets, usually shortened to CGT. The remaining gain of £110,000 minus £38,000, which equals £72,000, is rolled over into the new site. Its base cost becomes £262,000 minus £72,000, which equals £190,000, and the deferred slice waits there until the site is sold without replacement.

Notice the leverage hidden in the numbers. Marco kept back less than 13% of his proceeds, yet nearly 35% of his gain became taxable at once. The rule taxes retained cash pound for pound, and gains are usually much smaller than proceeds; therefore modest cash retention consumes relief quickly.

Worked Example Two: Keeping Too Much

Now consider Dana, who sells a unit for £300,000 with the same £190,000 cost and £110,000 gain, but downsizes into premises costing £180,000. Her retained cash is £120,000. Since the cash retained exceeds the entire gain, there is nothing left to defer: the full £110,000 is chargeable in the year of sale, no rollover claim is possible, and the new premises simply keep their £180,000 base cost. The relief has a hard edge, and it sits exactly where the retained cash equals the gain.

Key point: Full deferral needs full reinvestment of net proceeds. Partial reinvestment taxes the cash you kept, up to the whole gain. Reinvest less than your original cost and the relief disappears entirely.

Planning Around the Edge

Three practical thoughts follow. First, when a purchase price is negotiable, knowing the retained cash figure in advance lets you see the tax effect of every £10,000 of difference; occasionally a slightly larger premises is cheaper after tax than a slightly smaller one. Second, remember the timing flexibility from Part 1: the reinvestment window runs to thirty six months after the sale, so proceeds parked temporarily can still be fully reinvested later, with a provisional claim protecting the position meanwhile. Third, a partly taxable gain is not always bad news, because the chargeable slice can absorb your £3,000 annual exempt amount or capital losses that would otherwise sit idle. The aim is not maximum deferral; it is the lowest lifetime tax.

Action required: Before committing to the price of replacement premises, calculate proceeds minus reinvestment and compare it with your gain. That single subtraction tells you exactly how much tax falls due now, while the contract can still be shaped.

Key Takeaways

• The test compares reinvestment with sale proceeds, not with the gain; every pound of proceeds retained is taxable gain first.
• Disposal costs reduce the proceeds that need reinvesting; it is the net figure that counts.
• Retain less than the gain and the balance rolls over; retain more than the gain and the relief vanishes completely.
• The thirty six month reinvestment window and provisional claims give room to complete the spending later.
• A small chargeable slice can be useful, soaking up the annual exempt amount and losses; optimise the whole position, not just the deferral.

Deciding How Much to Reinvest?

One subtraction determines the tax, and it can still be shaped while the purchase is being negotiated. Zazentax can model the retained cash figure against your gain, your exempt amount and your losses, and find the reinvestment level with the lowest lifetime tax.

Run the numbers with Zazentax before you sign.