Contingent Consideration: s51 FA2003 Guide
Where part of the purchase price depends on a future event, s51 FA2003 requires SDLT to be paid immediately on the full assumed amount — including the contingent element. Refunds are available if the contingency never occurs, but timing rules are strict.
Last verified: March 2026
Key Takeaways
- •Under s51 FA2003, contingent consideration is assumed to be payable — SDLT must be calculated on the full amount at the effective date
- •If the contingency never triggers, an amended return can be filed within 12 months of the contingency falling away for a refund
- •If the refund window is missed (more than 12 months), Sch 11A FA2003 provides a separate relief claim route
- •Interest runs from the effective date of the transaction, not the date the contingency triggers or is assessed
- •Contingent consideration (s51) is distinct from uncertain consideration (s80) — the choice of provision has important practical consequences
In this article
What Is Contingent Consideration?
Contingent consideration arises where all or part of the purchase price for a property is conditional on a specified future event occurring or not occurring. The payment obligation exists, but it is dependent on something happening — for example, planning permission being granted, a tenant vacating, a business achieving certain turnover targets, or a remediation certificate being issued.
Section 51 FA2003 governs contingent consideration. The core rule is that for the purpose of calculating SDLT at the effective date of the transaction, contingent consideration is assumed to be payable. It does not matter that the event may never occur — at the moment of filing the return, HMRC requires you to include the contingent element in full.
Definition: Consideration is "contingent" if it is payable only if a stated event occurs or does not occur. The key is that you know the amount upfront — you just don't know whether it will be paid. If you don't know the amount either, the consideration may be "uncertain" under s80 FA2003 instead.
Treatment at the Return Date
The land transaction return (SDLT1) must be filed within 14 days of the effective date of the transaction (the date of completion, or exchange if earlier where both exchange and completion are notifiable). At this point, SDLT must be paid on the total assumed consideration, which includes:
- The fixed, certain base consideration
- The full contingent amount, assumed to be payable regardless of probability
HMRC's treatment is binary in terms of the assumption — you assume 100% of the contingent amount will be paid. There is no discounting for probability. A contingent payment of £100,000 that is only 10% likely to occur is still treated as £100,000 for SDLT at the effective date.
The full contingent amount must be included in the SDLT1 return filed within 14 days. Omitting it — even on the basis that you believe it is unlikely to be triggered — constitutes an incorrect return and may attract penalties and interest.
Worked Example: Planning Permission Contingency
A buyer purchases a property for £400,000, with a further £100,000 payable if planning permission for residential development is granted within 5 years of completion.
SDLT Calculation at Effective Date
What Happens Next
If planning IS granted
The contingency triggers. The buyer pays the £100,000 to the seller. No additional SDLT is due — it was already paid. The SDLT return does not need to be amended.
If planning is NOT granted (within 12 months of falling away)
File an amended SDLT return. SDLT is recalculated on just £400,000. HMRC refunds £5,000 (the excess SDLT paid).
Refund if Contingency Never Triggers
Section 51(3) FA2003 allows the buyer to amend the SDLT return within 12 months of the date on which it becomes clear that the contingency will not occur. The legislation refers to this as the date on which the consideration is "determined" or the contingency is "decided."
In the planning permission example, if the buyer receives a final refusal after 4 years and all appeal rights are exhausted, the 12-month clock starts from that determination date. The buyer files an amended SDLT1 on HMRC's online portal, recalculating SDLT on the base consideration only, and claims the refund.
The amended return must show the correct SDLT on the reduced consideration, and the refund is typically processed within 30 days of HMRC receiving the amended return, though complex cases may take longer.
Track the trigger date carefully. The 12-month window runs from the date the contingency definitively fails — not from the original effective date. If you miss this window, you must use the Sch 11A overpayment relief route instead, which is more complex and subject to different rules.
Outside the 12-Month Window (Schedule 11A)
Where the 12-month amendment window has closed, a taxpayer may still be able to reclaim overpaid SDLT through Schedule 11A FA2003, which provides a general relief for overpaid SDLT. This route has different conditions and a longer claim window (generally 4 years from the effective date of the original transaction under the standard Sch 11A provisions).
Schedule 11A claims are made by written application to HMRC and require supporting evidence that the contingency definitively did not occur and that SDLT was overpaid as a result. HMRC may require statutory declarations or formal evidence of the failure of the contingency.
If your contingency has a long time horizon (for example, a 10-year development overage clause), keep records of the original SDLT return and the full consideration breakdown. When the contingency fails, you will need this documentation to support the Sch 11A claim.
Distinction from Uncertain Consideration (s80)
Section 80 FA2003 applies where the amount of consideration is not yet ascertained at the effective date — for example, an overage clause where the amount depends on future rental income, number of planning units, or market values. The amount itself is unknown.
| Feature | s51 Contingent | s80 Uncertain |
|---|---|---|
| Amount known? | Yes — fixed sum if triggered | No — depends on future formula |
| Trigger known? | Conditional — event must occur | Likely to occur, amount unclear |
| Initial SDLT | Full amount assumed payable | Reasonable estimate used |
| Subsequent adjustment | Amended return within 12 months | Further return within 14 days of ascertainment |
| Interest runs from | Effective date | Effective date (original transaction) |
In practice, many complex consideration arrangements have elements of both contingency and uncertainty. The correct characterisation of the consideration type affects the initial SDLT calculation methodology and the procedure for subsequent adjustments. Specialist advice should be sought in any case where the consideration structure is not straightforwardly fixed.
Interest Accrual
Under both s51 (contingent) and s80 (uncertain) arrangements, interest on any underpaid SDLT runs from the effective date of the original transaction — not from the date the contingency triggers or the consideration is ascertained.
This is most relevant under s80, where the initial SDLT was calculated on an estimate and additional SDLT becomes due when the true amount is ascertained. HMRC will charge interest from the original effective date on the additional amount, even though the consideration was genuinely not known at that point. The interest is not a penalty but is statutory and cannot be appealed on the basis that the underpayment was not the taxpayer's fault.
Interest trap: On a large overage or earn-out, the interest running from the original effective date can represent a material cost. On a £500,000 additional consideration ascertained 5 years after completion, at HMRC's current late payment interest rate of ~7.75%, interest could easily exceed £150,000. Always model the interest cost when structuring deferred consideration arrangements.
Common Pitfalls
Conflating s51 with s80
Many advisers apply the wrong provision depending on the structure. If the amount is known but payment depends on an event, s51 applies and the full amount is assumed payable immediately. Applying s80 instead (treating it as uncertain) would give a different initial SDLT calculation. The wrong characterisation leads to either overpayment or, more dangerously, underpayment with interest.
Missing the refund window
The 12-month window for amending the return runs from the date the contingency definitively fails — not the original transaction date. Buyers sometimes confuse these dates and miss the amendment window, requiring the more complex Sch 11A route.
Not filing initially on the full assumed amount
Some buyers omit the contingent element from the initial SDLT return on the basis that the event "probably won't happen." This is an incorrect return. HMRC can raise an enquiry, charge the correct SDLT, plus interest and potential penalties for the incorrect return.
Frequently Asked Questions
How is contingent consideration treated for stamp duty?
Under s51 FA2003, contingent consideration is treated as if it will definitely be paid. You must include the full contingent amount in your SDLT calculation at the effective date of the transaction, regardless of how likely the contingency is to occur. SDLT is calculated on the total of fixed consideration plus the full contingent amount, and must be paid within 14 days.
Can I get a stamp duty refund if the contingency never happens?
Yes. If the contingency definitively fails — meaning the triggering event will no longer occur — you can amend your SDLT return within 12 months of the date the contingency falls away. HMRC will refund the excess SDLT paid. If you miss the 12-month window, a Schedule 11A overpayment relief claim is available within 4 years of the original effective date, though the process is more involved.
What is the difference between contingent and uncertain consideration?
Contingent consideration (s51) is where you know the amount but payment depends on a future event — for example, £100,000 extra if planning is granted. Uncertain consideration (s80) is where you know additional consideration will be paid but you don't know how much — for example, a percentage of future rental income. Under s51 you include the known amount in full. Under s80 you use a reasonable estimate and file a further return within 14 days of ascertainment.
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Emma Richardson, MRICS
Chartered Surveyor & Property Tax Specialist
Emma Richardson is a RICS-qualified Chartered Surveyor with over 12 years of experience in UK property taxation. She founded Stamp Duty Calculator to help buyers understand the complex world of property transaction taxes.