Staircasing Stamp Duty Calculator
Calculate SDLT on additional shared ownership shares bought after your initial purchase. Handles the 80% threshold rule, linked transactions, and lets you stress-test a sequence of future tranches.
Annexe, land or an old home not sold yet?
These are the purchases where a standard calculator can get your stamp duty wrong. Get it checked before you exchange.
The premium you paid for your initial share plus any earlier staircasing tranches. Once you go above 80% this total sets the SDLT rate for the transaction.
SDLT Payable
£0
New Total Ownership: 35%
Consideration
£25,000
Share Being Purchased
10%
At or below 80% there is no further SDLT to pay and no SDLT return to file, however much the share is worth.
Which calculator do I need?
Shared ownership has two distinct SDLT moments. Each has its own calculator.
| Your situation | Use this | What it does |
|---|---|---|
| Buying my first share of a shared ownership home | Shared Ownership Calculator | Compares the market value election against paying SDLT only on the initial share. Includes FTB relief. |
| Already a shared owner, buying more shares (staircasing) | Staircasing Calculator You are here | Calculates SDLT on each additional tranche, flags the 80% threshold, and applies the linked transactions rule when you cross it. |
| Staircasing in a single jump to 100% ownership | Either works. Start here, then see the final staircasing guide | A single transaction crossing 80% and reaching 100% triggers one linked-transaction SDLT calculation, covered here. |
Quick rule of thumb: if you have not yet completed your initial shared ownership purchase, you are on the wrong page. Use the shared ownership calculator instead. The staircasing calculator is for the second purchase onwards. For the underlying rules rather than a number, see how stamp duty on shared ownership works across both the market-value election and the staged route.
How staircasing SDLT works
Under the default staircasing election (the one you ended up with if you did not tick “market value election” on your SDLT1 at initial purchase), HMRC sets out a very specific rule for further SDLT on additional share purchases. GOV.UK guidance is unambiguous: “If you buy more shares in a property... until your share reaches more than 80%, you don’t pay any more SDLT or tell HMRC about the transactions in a SDLT return.”
Cumulative share ≤ 80%
No further SDLT on staircasing tranches. No SDLT return required. Buy as many additional shares as you like, in any size, with zero SDLT impact.
The transaction that crosses 80%
This tranche is treated as linked with every earlier staircasing purchase. SDLT is calculated on the cumulative consideration paid for all linked share purchases.
Every tranche after 80%
Each subsequent staircasing transaction is also linked. SDLT is recalculated on the new cumulative total, with SDLT already paid credited against the new liability.
SDLT is calculated on consideration, not market value
After crossing 80%, the linked-transaction calculation uses the actual cumulative consideration paid for the property to date, applied to standard SDLT rate bands. It is not a market value re-rating. The initial share premium counts towards that total, but where the lease was granted on or after 12 March 2008 the first grant is excluded from the linked group, so no extra tax falls due on the premium itself. For leases granted before that date, a further return and further tax on the original premium can be required under section 81A Finance Act 2003.
2026 SDLT rate bands applied to staircasing
When SDLT does become payable on a staircasing transaction (only after crossing 80% under the staircasing election), the calculator applies the current residential SDLT bands to the cumulative linked consideration. These are the bands in force from 1 April 2025:
| Portion of consideration | Standard rate | With higher rates (additional property) |
|---|---|---|
| Up to £125,000 | 0% | 5% |
| £125,001 – £250,000 | 2% | 7% |
| £250,001 – £925,000 | 5% | 10% |
| £925,001 – £1.5m | 10% | 15% |
| Above £1.5m | 12% | 17% |
Bands per GOV.UK SDLT rates. The 5% additional dwelling surcharge applies if you already own another property anywhere in the world at the effective date of the staircasing transaction.
Worked examples
Three scenarios on a property worth £400,000 at the time of each staircasing transaction, where the buyer originally took a 40% share for £160,000. All assume the default staircasing election (no market value election made at initial purchase), a lease granted on or after 12 March 2008, no additional property surcharge and no FTB relief.
| Scenario | Current share | Buying | New cumulative | Consideration | SDLT on this tranche |
|---|---|---|---|---|---|
A. Below 80% Routine staircasing tranche | 40% | +25% | 65% | £100,000 | £0 |
B. Crossing 80% Trigger transaction: all prior staircasing tranches now linked | 65% | +25% | 90% | £100,000 | £2,222 £8,000 on the £360k linked total, apportioned 100:360 |
C. After 80% Final staircasing to 100% | 90% | +10% | 100% | £40,000 | £1,278 £1,000 on this tranche plus £278 more on tranche B |
How scenario B works: the rate is set by everything paid for the property so far, which is the £160,000 initial premium plus both £100,000 staircasing tranches, £360,000 in total. Standard SDLT on £360,000 is £8,000 (0% on the first £125,000, 2% on the next £125,000, 5% on the remaining £110,000). That total is then apportioned across the linked transactions in proportion to what each one cost, so this tranche bears £8,000 × 100,000 / 360,000 = £2,222. Because the lease was granted on or after 12 March 2008, no further tax falls due on the original premium, and the sub-80% tranche is not taxed either.
How scenario C works: the total paid to date is now £400,000 and standard SDLT on that is £10,000. This tranche bears £10,000 × 40,000 / 400,000 = £1,000. Tranche B is recalculated against the new total at £10,000 × 100,000 / 400,000 = £2,500, and £2,222 has already been paid, so a further £278 is due on it. Total payable at this point: £1,278.
When should you staircase?
Going straight to 100%
A single staircasing transaction from your current share to 100% triggers exactly one SDLT calculation under the linked-transactions rule. This is often the simplest path: one valuation, one solicitor instruction, one SDLT return. See the final staircasing guide for the legal mechanics.
Staircasing in stages
Multiple tranches under 80% are SDLT-free, but each one over 80% is a separate linked-transaction recalculation with its own SDLT return and 14-day deadline. If you plan to staircase beyond 80%, sequencing each step matters. Use the calculator to model a 2-step plan vs a 3-step plan.
Holding below 80%
If you stay at or below 80%, you never trigger any further SDLT under the staircasing election. Some owners stair-case to a comfortable level (e.g. 75%) and stop, the trade-off is rent on the remaining share vs the SDLT savings from never crossing the threshold.
Rising property value
Each tranche is priced on a current RICS valuation. If the property value is rising, the same percentage costs more each time. The calculator lets you model different future valuations to see how price movement changes the SDLT cost of a 2025 vs 2027 staircasing decision.
Frequently asked questions
Do you pay stamp duty when staircasing?
Only sometimes. If you made a market value election at your initial shared ownership purchase, no SDLT is ever due on staircasing. Under the default staircasing election, tranches that keep your cumulative ownership at 80% or below do not require any further SDLT or SDLT return. SDLT re-engages on the transaction that takes you above 80%, and that transaction is linked with all earlier and subsequent staircasing tranches.
How is this calculator different from the shared ownership calculator?
The shared ownership calculator is for your initial purchase: it compares the market value election against paying SDLT only on the first share you buy. This staircasing calculator is for what comes next: buying additional shares from the housing association after that initial purchase. It handles the 80% threshold rule and the linked-transactions calculation that the initial-purchase calculator does not need to consider.
What is the 80% threshold in shared ownership staircasing?
The 80% threshold is the point at which SDLT rules change under the staircasing election. While your cumulative ownership stays at 80% or below, no further SDLT is due on staircasing tranches. The transaction that takes you above 80% is the trigger: it is linked with the earlier purchases under FA 2003, the rate is set by everything paid for the property to date including the initial premium, and the resulting tax is apportioned across the linked transactions in proportion to what each one cost.
Does the calculator handle the linked transactions rule after 80%?
Yes. Once a staircasing transaction crosses the 80% line, the calculator adds the amount you have already paid for the property to the price of the new share, applies the standard SDLT rate bands to that linked total, and then apportions the tax so that this transaction bears only its own share of it. Each later staircasing transaction raises the total again, so earlier post-80% tranches are recalculated and topped up under section 81A Finance Act 2003.
What share size should I use in the calculator?
Enter the additional share you are buying as a percentage of the full property, not as a percentage of the housing association share. For example, if you currently own 40% and are buying another 20%, enter 20%. Use a current RICS valuation for the full property value, because each staircasing purchase is priced on the market value at the time of the transaction, not the value when you first bought your share.
Does first-time buyer relief apply to staircasing?
First-time buyer relief is only available at the initial purchase, not on staircasing. If you claimed FTB relief on your initial share, you have already used the relief. Staircasing tranches are assessed on the consideration paid for the additional share using standard SDLT rate bands, with no FTB carve-out, regardless of whether your initial purchase qualified for relief.
Is staircasing notifiable to HMRC?
No while your cumulative ownership stays at 80% or below: HMRC specifically excludes those staircasing tranches from the SDLT return requirement. Yes once a transaction takes you above 80%, and on every staircasing transaction afterwards. Notifiable transactions require an SDLT1 return filed within 14 days of the effective date, usually handled by your solicitor.
Reviewed by
Julie White
ACAStamp duty specialist since 1999Stamp Duty Land Tax Specialist
ACA and Tax Adviser with a career spanning nearly four decades, specialising in stamp duty planning and advisory work since 1999.