SEIS Investor Guide 2026: Tax Reliefs Explained

Quick answer

For 2026/27, the Seed Enterprise Investment Scheme (SEIS) lets a UK investor claim 50% income tax relief on up to GBP 200,000 of qualifying new shares, a maximum tax reduction of GBP 100,000. Hold the shares three years and any gain is free of capital gains tax, with loss relief and reinvestment relief available too. The trade-off is high risk: these are early-stage companies and you can lose everything.

What SEIS is and why it exists

SEIS is one of four venture capital schemes the UK government uses to channel private money into small, growing companies. It targets the very earliest stage, where the risk of failure is highest and ordinary investors would otherwise be reluctant to put in capital. To compensate for that risk, SEIS offers the most generous reliefs of any of the schemes.

The logic is simple. Seed-stage companies struggle to raise money because most fail. By cutting the investor's effective cost through tax relief, the government makes the risk-reward balance more attractive, so more capital flows to start-ups. In return, both the company and the investor must meet detailed conditions, and HMRC polices them closely.

SEIS sits below the Enterprise Investment Scheme (EIS). A typical journey is an SEIS round first, then EIS as the company grows. They are separate schemes with separate limits, and you can use both over a company's life, but not double-count the same investment.

The four SEIS reliefs

SEIS bundles several reliefs. Understanding each one, and how they interact, is the key to the scheme.

Income tax relief

The headline benefit is 50% income tax relief on the amount invested. Invest GBP 20,000 and you can cut your income tax bill by GBP 10,000. The relief is capped at your actual income tax liability for the year -- you cannot turn a GBP 5,000 tax bill into a refund by claiming GBP 6,000 of relief.

This matters most for people paying higher or additional rate tax. If you are in the 40% or 45% band, or caught in the 60% effective band between GBP 100,000 and GBP 125,140 where the Personal Allowance tapers away, you are likely to have enough income tax liability to absorb the full relief. Use the

to work out your liability before deciding how much to invest.

You can also carry back an SEIS investment to the previous tax year, treating it as if made then. This is useful if you have unused SEIS allowance from last year, or if last year was a higher-tax year.

Capital gains tax exemption

If you hold the shares for at least three years and the income tax relief was given and not withdrawn, any gain when you sell is exempt from capital gains tax. Given that CGT rates for 2026/27 are 18% within the basic-rate band and 24% above it, this exemption can be valuable on a successful exit. It is entirely separate from your GBP 3,000 Annual Exempt Amount, which still covers your other disposals.

Reinvestment relief

Separately, if you have a chargeable gain from selling another asset and you reinvest it into SEIS shares, you may exempt part of that gain from CGT. This reinvestment relief is distinct from the CGT exemption on the SEIS shares themselves. The two can apply to the same investment: the gain you rolled in is sheltered, and the future gain on the SEIS shares is also exempt if you hold for three years.

Loss relief

Because so many seed companies fail, loss relief is central to SEIS. If your shares become worthless or you sell at a loss, the allowable loss is what you invested minus the income tax relief you already received. You can then set that loss against income or capital gains.

Here is how the downside works on a GBP 10,000 investment that fails completely, for a 45% additional-rate taxpayer claiming loss relief against income:

So a GBP 10,000 investment that goes to zero costs this investor GBP 2,750 net. The figures change with your marginal rate, but the principle holds: the reliefs sharply reduce, though do not eliminate, the cost of failure. Model your own CGT position with the

.

Limits and key conditions

The reliefs come with conditions on both you and the company. Get them wrong and HMRC can withdraw relief already claimed.

Investor limits

• The maximum SEIS investment qualifying for relief is GBP 200,000 per tax year, giving up to GBP 100,000 of income tax reduction.
• You must hold the shares for at least three years from issue, or from when the company starts trading if later.
• You generally cannot be connected with the company, broadly meaning an employee, or someone who with associates controls more than 30% of the shares, votes or assets. Some directors can still qualify.
• The shares must be new ordinary shares, paid for in full in cash, carrying no special preferential rights.

Company conditions

The company must also qualify. The rules cover how young and small the company is, the trade it carries on, how much it has already raised under venture capital schemes, and how it uses the money. Several trades are excluded. Companies usually apply to HMRC for advance assurance before a round, which gives investors comfort that the shares should qualify. Because these company-level thresholds change and are detailed, confirm the current figures on the gov.uk SEIS guidance rather than relying on memory.

SEIS versus EIS at a glance

The EIS investment limit and company conditions are not on our verified rate card, so check gov.uk for the current EIS figures before committing.

How to claim SEIS relief

You cannot claim until the company issues you an SEIS3 certificate. The company can only do this once HMRC has authorised it and the qualifying trading period has been met, which is typically several months after you invest. The certificate carries a unique reference number you need for the claim.

With the SEIS3 in hand, you claim through your Self Assessment tax return. In some cases HMRC can adjust your tax code or accept a standalone claim, but Self Assessment is the usual route. Keep the certificate safe -- without it you cannot claim. If you are carrying back relief to the previous year, you make that election as part of the claim.

Where SEIS fits in a wider plan

SEIS is a niche, high-risk allocation, not a core holding. It works best as a small slice of a portfolio for someone who has already used more mainstream, tax-efficient wrappers. Before considering SEIS, most people should make full use of their GBP 20,000 ISA allowance and their pension Annual Allowance of GBP 60,000, both of which are far lower risk.

Because SEIS relief is capped at your income tax liability, it suits higher earners with substantial tax bills and the capacity to lose the money invested. If a single failed start-up would damage your finances, SEIS is probably not for you. Spreading smaller amounts across several SEIS companies, often via a managed fund, is a common way to diversify the high failure risk.

The bottom line

SEIS offers the most generous tax reliefs in the UK venture capital landscape: 50% income tax relief on up to GBP 200,000 a year, a CGT exemption on successful exits, reinvestment relief and loss relief on failures. Those reliefs meaningfully cut both the cost of investing and the cost of failure. But they exist precisely because the underlying companies are so risky. Treat SEIS as speculative money you can afford to lose, confirm the detailed company conditions on gov.uk, and take professional advice before you commit.