Exchange and completion: what happens, when, and what can go wrong

Before exchange: nothing is binding

This surprises many first-time buyers: from offer acceptance right up to the moment of exchange, either side can walk away without penalty. The seller can accept a higher offer (gazumping); the buyer can lower theirs (gazundering) or vanish entirely. All the weeks of conveyancing happen in this legally unprotected zone — which is exactly why speed matters.

What happens at exchange

Despite the name, nothing physical is exchanged any more. The two conveyancers hold identical signed contracts and “exchange” them in a recorded phone call, reading the contracts aloud to confirm they match — a ritual called formula B that has outlived the paperwork it referred to. At that moment:

• The sale becomes legally binding on both sides
• Your deposit (usually 10% of the price) is transferred to the seller's side
• The completion date written into the contract is fixed
• The buyer becomes responsible for insuring the building — your buildings insurance must start today, not at completion

Pull out after exchange and you lose the deposit, and can be sued for further losses. This is the point of no return — for the seller too.

The gap between exchange and completion

Typically one to two weeks — enough time to book removals with certainty, since the date is now legally fixed. Same-day exchange and completion is possible and increasingly common in chain-free deals, but it means booking removals for a date that isn't certain until the morning it happens.

What happens on completion day

1. Your lender releases the mortgage money to your conveyancer (often the day before)
2. Your conveyancer sends the full purchase money to the seller's conveyancer
3. The seller's side confirms receipt — usually between midday and 2pm
4. The seller's conveyancer authorises the estate agent to release the keys
5. You collect the keys; the house is yours

In a chain, this sequence happens in order up the chain — each completion funds the next — which is why keys for the top of a chain sometimes aren't released until late afternoon. Sellers must be fully moved out by the contractual completion time, usually 1pm or 2pm.

Afterwards, your conveyancer pays your stamp duty to HMRC and registers your ownership with the Land Registry. The registration confirmation can take weeks to months to arrive; that's normal.

What can go wrong (and how to avoid it)

• A chain collapse before exchange — the most common failure. Mitigation: push everyone towards the earliest possible exchange; the unprotected period is the risk
• Mortgage offer expiry — offers last ~6 months; slow transactions can outlive them. Watch the date and ask for an extension early
• Completion-day money delays — a late bank transfer somewhere in the chain can push completion to the next working day. Painful but rare; avoid Fridays if you want slack
• Failure to complete after exchange — very rare, because the penalties are severe: notices to complete, interest, forfeited deposits and lawsuits. Exchange is taken seriously precisely because it works