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by Undo Capital
December 15, 2025
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What Is the SEIS3 Certificate?

A SEIS3 certificate is the document issued by HMRC that allows investors to formally claim their Seed Enterprise Investment Scheme (SEIS) tax relief.

SEIS3 Certificate Meaning

The SEIS3 certificate's meaning centres on enabling investors to access SEIS tax benefits after the company’s compliance has been approved. To define the SEIS3 certificate in practice, HMRC issues it once a company’s SEIS1 form is accepted, confirming that the investment qualifies for relief. Each investor receives their own SEIS3, which they submit with their tax return to claim income tax relief, capital gains reinvestment relief and potential loss relief. A clear SEIS3 certificate definition is essential because, without this document, investors cannot obtain any SEIS tax advantages. The SEIS3 stands for the final approval step that unlocks early-stage tax incentives.

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Disclosure Notice: This communication is issued by Undo Capital Limited (“Undo Capital”) and is provided strictly for informational purposes only. It contains general information and should not be relied upon as accounting, business, financial, investment, legal, tax, or other professional advice. Undo Capital is not regulated by the Financial Conduct Authority (FCA) and does not provide investment, financial, or tax advice. Our services are designed to assist startups and businesses with company formation, legal agreements, and funding-related documentation. Nothing in this communication constitutes, or should be construed as, a recommendation, offer, or solicitation to purchase or sell any security or financial instrument.
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Disclaimer: Our services are designed to assist startups and businesses with company formation, legal agreements, and funding-related documentation. We do not provide investment advice, financial advice, or tax advice, nor are we regulated by the Financial Conduct Authority (FCA). Participating in startups and early-stage enterprises carries inherent risks, including limited liquidity, absence of dividends, potential loss of investment, and dilution. Any decisions regarding investments should be made independently by the investor as part of a well-diversified portfolio.