When does our CGT liability begin

We’re in the process of selling a property which has the potential of exchanging contracts in this tax year and completing in the following one. On exchange a deposit is paid by the buyer and held in our solicitors account until completion when all the funds are transferred to us. Are we liable for CGT on the deposit, which is ours but not held by us, or only when the whole balance goes into our account.

Hi

You can calculate your capital gain arising from the disposal of the property, when you have completed the sale, as the sale may fall through before that date.  
Capital Gains Tax liability arises in the tax year that the completion of the disposal occurs.  
Any early payments, such as deposits are chargeable to Capital Gains Tax, as part of the disposal value in the tax year of completion.

Thank you