How to claim SEIS relief on your tax return, step by step

In short: you claim SEIS relief using the SEIS3 certificate issued by the company, entering the details in the additional information pages of your self assessment return, or by completing the claim section on the certificate and sending it to HMRC. The process is set out in HMRC helpsheet HS393.

What you need in front of you

• The SEIS3 certificate for each investment.
• The company's name and HMRC unique investment reference from the certificate.
• The date the shares were issued and the amount subscribed.
• Your self assessment login, or your accountant's details.
• Details of any chargeable gain if you are also claiming reinvestment relief.

If you do not file a self assessment return

You can claim by completing the claim form on page three of the SEIS3 certificate and posting it to HMRC. HMRC will normally adjust your PAYE code or make a repayment. This route is slower than a return but perfectly valid.

Deadlines

The claim must be made no more than five years after 31 January following the tax year in which the shares were issued. For shares issued in 2025 to 2026, that is 31 January 2032. In practice, claim as soon as the certificate arrives.

Claims that come later

Two further claims may follow years afterwards: loss relief if the company fails, and disposal relief when you sell at a gain. Both depend on the original income tax relief having been claimed and kept, which is the strongest argument for making the claim promptly.