Once contracts are exchanged, both parties are legally committed to a fixed completion date. On that day, the buyer's solicitor transfers the outstanding balance to the seller's solicitor. The moment those funds are received, legal title passes to the buyer and the keys are released. The gap between exchange and completion is typically a few weeks, though it can be shorter or longer by agreement.
Completion triggers several immediate obligations. Stamp Duty Land Tax becomes payable within a set period after completion, and overseas buyers must also account for the non-resident surcharge where applicable. The conveyancing solicitor then registers the change of ownership at Land Registry. For off-plan purchases, completion depends on the developer finishing the build, so delays can push the date back, which has implications for mortgage offers with expiry dates.
As a simple example: a buyer purchases a flat for £500,000, paying a ten percent deposit on exchange. On completion day, their solicitor sends the remaining £450,000 to the seller. Keys are handed over immediately, and the buyer is now the legal owner.
For overseas investors, completion day is when SDLT and the non-resident surcharge fall due and when currency must arrive in sterling on time; misaligning completion with a mortgage offer expiry or an international transfer delay can jeopardise the entire purchase.