How to Claim SEIS Tax Relief and Carry It Back
Claim SEIS income tax relief using SEIS3, choose the issue year or preceding year, check your tax capacity and avoid common carry-back errors.
Written by Steve Livingston LLB FCA, IP Tax Solutions. Technical content reviewed 21 September 2026.
You can claim SEIS income tax relief after receiving a valid SEIS3 certificate from the company and checking that you meet the investor conditions. Relief is normally claimed for the tax year in which the shares were issued. You can elect to treat some or all of the qualifying subscription as made in the immediately preceding tax year.
Carry-back changes the income tax allocation. It does not move the actual share issue date, shorten the holding period or remove the need for a certificate. This guide concerns the investor's claim. Companies needing to issue certificates should use our SEIS1, SEIS2 and SEIS3 guide.
How much SEIS relief can you claim?
The current income tax reduction is 50% of the eligible subscription. The annual investment limit is £200,000, with the relief restricted to available income tax liability. The legal basis is ITA 2007 s.257AB. The increased limit applies from 6 April 2023; an older claim needs the rules for its relevant year.
You cannot receive more relief than the tax available to reduce. A repayment of tax already paid may result, but SEIS is not a payment of the headline relief regardless of your tax position. Unused relief cannot simply be carried forward.
Step 1: obtain and check your SEIS3
The company issues SEIS3 after HMRC authorises it. An advance-assurance letter, share certificate or bank transfer is not a substitute. Check the investor name, issue date, amount subscribed, company and Unique Investment Reference. Keep the supporting investment documents too.
Check your own investor eligibility. A company meeting its conditions does not establish yours. Founder ownership, associates, employment, loans and benefits received can all require investigation.
Step 2: compare the two tax years
For shares issued in 2026/27, the ordinary claim is for 2026/27 and the carry-back option is 2025/26. You cannot elect to carry those shares back to 2024/25. Consider the SEIS subscriptions already allocated to each year, income tax remaining after other reliefs and whether you also need capital-gains reinvestment relief.
The election can cover part of an issue. Keep a schedule showing the subscription allocated to each year and make sure the same amount is not claimed twice.
Carry-back example
An investor subscribes £40,000 for qualifying shares issued on 1 October 2026. Assume they have sufficient unused SEIS annual capacity, £12,000 of available income tax liability in 2025/26 and £8,000 in 2026/27.
| Allocation | Subscription | Income tax reduction at 50% |
|---|---|---|
| Carry back to 2025/26 | £24,000 | £12,000 |
| Retain in 2026/27 | £16,000 | £8,000 |
| Total | £40,000 | £20,000 |
This illustrates the allocation, assuming all conditions are met and relief is retained. The actual holding period still runs from 1 October 2026. Your tax calculation may contain other reliefs and interactions that change the best allocation.
Step 3: make the claim through the appropriate route
For relief in the year the shares were issued, include the SEIS subscription in the relevant section of your Self Assessment return and give the required investment details. Use that year's return notes rather than relying on an old box number.
For a claim relating to shares issued in a different tax year, use the claim section of the SEIS3 certificate and follow HMRC's instructions. This is particularly important for carry-back. Do not assume that putting the later subscription into an earlier return's ordinary current-year SEIS box makes a valid election.
HMRC's HS393 helpsheet explains the claim route. For current-year relief, an adjustment to a PAYE code or payments on account may also be possible after the certificate is received. Explain any provisional figures and retain evidence of the claim.
What is the SEIS claim deadline?
The deadline is normally five years after 31 January following the relevant tax year. For shares issued in 2026/27 and claimed for that year, it is 31 January 2033. However, s.257EA(2) treats a carried-back part as a separate issue in the preceding year for this purpose. For the part carried back to 2025/26, the deadline is therefore 31 January 2032. Carry-back can bring the deadline forward.
This is different from the usual deadline for amending a tax return. Check the deadline for each allocation and do not wait until it expires to obtain the certificate or establish the available relief.
How does carry-back affect capital gains relief?
The year used for the income tax relief also matters when matching an investment with gains for SEIS reinvestment relief. A carry-back election can therefore affect two taxes. Model the income tax and capital-gains positions together before deciding the allocation. Our SEIS capital gains and reinvestment guide gives a dated example.
What if the investment loses value?
That is a separate question from claiming the initial 50% relief. An allowable share loss may support a further claim, but the amount must reflect income tax relief retained and the share-loss conditions. See our loss relief guide.
Questions investors often ask
Can I claim before SEIS3 arrives?
No. Wait for the compliance certificate and check it before making the claim.
Can I use two previous years?
No. SEIS income tax carry-back is to the immediately preceding tax year. Different timing provisions apply to a later share-loss claim.
Can I carry forward a shortfall?
No. Review the issue year and preceding year before claiming; there is no general carry-forward of unused SEIS income tax relief.
Need help with SEIS?
IP Tax Solutions advises founders, investors and their professional advisers on SEIS eligibility, investment terms, compliance and claims. See our SEIS and EIS advisory service or contact Steve with the facts and relevant dates.
