SDLT on shared ownership staircasing

Looking for a solve on how much SDLT I'd have to pay when staircasing my shared ownership property. I failed to get an answer on the phone to HMRC and have had various answers previously. I bought 50% of a property in 2019 and elected not to pay SDLT at the time. I now want to purchase the remaining 50%. Purchase 1 = 50% share, £180,000 of 360,000 total value at time. Purchase 2 = 50%, £200,000 of £400,000 current total value. By my calculations, total purchase are 180k + 200k = 380k, meaning 6,500 SDLT (full amount before fractioning). Apportioned by: 200,000/380,000 = 0.526 x 6,500 = £3,421 SDLT due. Can anyone tell me if this is correct? Thanks!

Hi,

You will need to contact The Stamp Duty Land Tax team for advise.

Stamp Duty Land Tax

Thank you.