This part of GOV.UK is being rebuilt – find out what beta means

HMRC internal manual

Inheritance Tax Manual

Lifetime transfers: gifts in consideration of marriage or registration of civil partnership: IHTA restriction of Rennell - payments under covenant

A sum covenanted to be paid in a marriage or civil partnership (IHTM11032) settlement qualifies for exemption when it is paid (assuming the conditions for exemption are satisfied).

If the covenantor dies before making payment however, it is not deductible from their estate.