The completion date is written into the contracts and so this must be in place for the solicitors to be able to do the final checks before exchange of contracts can take place. Who decides completion date? Both parties collectively decide and agree on the completion date.
Who decides on a completion date?
As a first step, a seller might, for instance, retain the buyer's deposit and instruct his agent to remarket the property. It's therefore sensible that the completion date is set with regard to a realistic time frame and is some time after exchange of contracts.
When should your completion date be?
Traditionally, completion is arranged to happen anywhere from seven to 28 days after exchanging contracts. However, exchanging and completing on the same day is not unheard of. It's faster, and it eliminates the need to pay a deposit on the exchange of those contracts.