How Does SEIS Tax Relief Work? The Complete 2026 Guide for UK Investors

Author: Hugo Vaux
Last updated: February 2026

This guide is for educational purposes only and does not constitute tax or investment advice. Tax treatment depends on individual circumstances and may change. Investors should consult their tax adviser before making decisions.

What Is SEIS?

The Seed Enterprise Investment Scheme, or SEIS, is a UK government initiative designed to encourage investment into very early-stage, high growth companies by offering generous tax reliefs to investors.

SEIS is not simply a tax benefit. It is a government policy tool designed to stimulate innovation and entrepreneurship by sharing part of the early stage investment risk with investors.

For eligible UK taxpayers, SEIS provides:

50% income tax relief on investments of up to £200,000 per tax year
Capital Gains Tax reinvestment relief
Capital Gains Tax exemption on qualifying disposals after three years
Loss relief if the investment fails

Together, these reliefs can materially reduce downside exposure, but they do not remove investment risk.

What Tax Reliefs Does SEIS Offer?

There are four core tax benefits under SEIS.

1. 50% Income Tax Relief

You can claim income tax relief equal to 50% of the amount invested, on a maximum investment of £200,000 per tax year. Relief cannot exceed the income tax you owe.

You can usually claim relief in the tax year the shares are issued, or elect to carry back to the previous tax year, subject to conditions. You cannot claim SEIS income tax relief until you receive a valid certificate (called an SEIS3) from each investee company.

2. Capital Gains Tax Reinvestment Relief

If you reinvest a chargeable capital gain into qualifying SEIS shares, you can usually treat 50% of that gain as not chargeable to Capital Gains Tax.

Because the maximum SEIS investment eligible for income tax relief is £200,000 per tax year, the maximum gain that can typically be relieved in a tax year is £100,000.

If you invest less than the gain realised, the exemption is limited to 50% of the amount invested.

To qualify, you must also be entitled to SEIS income tax relief on the same shares.

3. Capital Gains Tax Free Growth

If you hold SEIS shares for at least three years and the qualifying conditions are met, any gain on disposal may be exempt from Capital Gains Tax.

For example, if you invest £100,000 and later sell for £300,000, the £200,000 gain may be free from Capital Gains Tax, assuming SEIS conditions have been satisfied throughout.

4. Loss Relief

SEIS investments are high risk and many early-stage companies fail. If that happens, you may be able to claim loss relief.

Your loss is calculated after deducting any income tax relief already received. That loss can usually be offset against capital gains, or potentially against income.

For example:

Investment: £100,000
Income tax relief: £50,000
Net capital at risk: £50,000
If loss relief is claimed against income at 45%*, further relief of £22,500 may be available
Effective economic loss: £27,500

*If loss relief is claimed against income, the value of relief depends on the investor’s marginal rate for the year of claim. This example is based on an additional rate taxpayer with a marginal income tax rate of 45%.

The value of loss relief depends on your marginal tax rate and individual circumstances.

How Do You Claim SEIS Relief?

There are three practical steps that matter most:

The company (or underlying companies in a fund) must qualify for SEIS and submit the required compliance statement to HMRC.
You must receive an SEIS3 certificate from each investee company before you can claim SEIS income tax relief. In practice, SEIS3 certificates are usually issued a few months after each underlying investment.
Relief is then claimed through your Self-Assessment return or, in some cases, via your tax code.

If you invest through an SEIS fund that deploys capital over time, you will typically receive SEIS3 certificates progressively for each underlying investment.

How Investors Access SEIS in Practice

There are two broad ways to access SEIS. You can invest directly into individual SEIS-qualifying companies, or you can invest through a professionally managed SEIS fund.

Investing directly offers greater control and selectivity, but it also requires you to source opportunities, conduct your own due diligence, negotiate terms and manage the documentation and ongoing monitoring yourself.

A diversified SEIS fund, by contrast, provides exposure across multiple early stage companies within a structured portfolio. It typically offers professional selection, disciplined portfolio construction, consolidated reporting and administrative coordination, including the handling of SEIS3 certificates. For many high net worth investors, diversification, disciplined selection and professional oversight are central to managing risk at the seed stage, where failure rates are inherently high.

The Guinness Founders SEIS service

Guinness Ventures operates the Guinness Founders SEIS service, which invests across a portfolio of SEIS qualifying early stage businesses and is designed for UK taxpayers seeking SEIS tax relief alongside diversification. Learn more about the Guinness Founders SEIS service.

SEIS vs EIS vs VCT: What is the difference?

SEIS is often compared with the Enterprise Investment Scheme (EIS) and Venture Capital Trusts (VCTs), as all three are UK tax-efficient investment structures. SEIS offers the highest upfront income tax relief but applies to the earliest stage, highest risk companies. For a comparison of EIS and VCT structures, see our EIS and VCT Tax Efficiency Guide.

Frequently Asked Questions

Is SEIS relevant for additional rate taxpayers?

For additional rate taxpayers, SEIS can be particularly powerful because of the combination of 50% upfront income tax relief and the ability to claim loss relief against income at the marginal rate.

If an investment fails, the effective economic loss can be significantly lower than the amount invested, depending on how loss relief is claimed. That said, SEIS should not be viewed purely as a tax mitigation tool. The underlying companies are very early stage and high risk. The tax relief improves the risk-reward profile, but it does not remove investment risk.

Can I invest in both SEIS and EIS in the same tax year?

Yes. SEIS and EIS have separate annual investment limits and operate under different parts of the legislation. It is common for experienced investors to use SEIS for earlier stage exposure and EIS for later stage growth companies within the same tax year, depending on their allocation strategy and risk appetite.

Which tax year can I claim the 50% income tax relief against?

You can usually claim relief in the tax year the shares are issued, or you can elect to carry back to the previous tax year, subject to annual limits and your available income tax liability. You can only claim SEIS income tax relief once you have received an SEIS3 certificate. In practice, this is usually issued a few months after the investment, once HMRC has approved the company’s compliance statement. Regardless of when the certificate arrives, the date of share issue is the key factor.

If a SEIS fund invests in 2026/27, can I reduce a gain from 2025/26?

Potentially yes, but only if you elect to carry back some or all of that SEIS investment so it is treated as issued in 2025/26 for SEIS income tax relief purposes. When you carry back for income tax relief, SEIS reinvestment relief follows that same “treated as issued” year, meaning it can line up with gains in 2025/26.

What happens if the investment fails?

SEIS is designed for very early stage, high risk businesses. You should be prepared to lose some or all of your capital. If a company fails and your shares become of negligible value or are disposed of at a loss, you may be able to claim loss relief.

Your capital loss is calculated after deducting any income tax relief already received, and that loss can usually be set against capital gains. Alternatively, it may be possible to offset the loss against income, which can materially reduce the effective downside, depending on your marginal rate of income tax. The availability and value of loss relief therefore depends on your personal tax position.

Key Risks

SEIS investments are high risk and illiquid. Companies may fail and investors may lose some or all of their capital. Tax reliefs depend on meeting legislative conditions and may be withdrawn if those conditions are breached.

Don't invest unless you're prepared to lose all the money you invest. This is a high-risk investment and you are unlikely to be protected if something goes wrong. Take 2 minutes to learn more.