you'd

No — say "If you'd known". In conditional sentences, 'you'd' (you had) is followed directly by the past participle, not by 'have'.

Definition

pron. a short way of saying 'you would' or 'you had'. You use it to talk about something that might happen or something you did in the past.

pron. the contracted form of 'you would' or 'you had'. Functions as a subject-auxiliary cluster in spoken and informal written English.

simple

“I think you'd really like this movie.”

contextual

“If you'd told me you were coming, I would have prepared some dinner for us.”

complex

“You'd be surprised how many people forget to check their passports before heading to the airport for an international flight.”

The meaning depends on the following verb: followed by a base verb, it means 'you would'; followed by a past participle, it means 'you had'.

If you'd have known

If you'd known

In conditional sentences, 'you'd' (you had) is followed directly by the past participle, not by 'have'.

you'd likeyou'd expect