When does the iddat begin for a woman who is given Talaaq?

Answer

Once the husband issues Talaaq Baa-in whether verbally or in written form, then it will immediately terminate the marriage. The Iddat begins from the very moment Talaaq Baa-in is issued. The Iddat is a period of three full menstrual cycles.

If he issues only a Talaaq without stating 'Baa-in', then such Talaaq can be revoked by the husband within the Iddat period. After expiry of Iddat he can no longer revoke it. It will then be final. To revoke the Talaaq he need only say that he has revoked it or taken back his wife or act with her in a manner in which husband and wife have relationship.