Yes, usually. This situation commonly arises where a person didn’t realise they’d need a certificate at the time, or when there’s a delay getting a doctor’s appointment. Backdated certificates may be issued at the doctor’s discretion, depending on your situation:

• Often, this can cover a few days into the past.
• The date of the appointment always appears at the top of the document, but the earlier dates can be certified as the period of absence/ carer’s leave.
• If your work absence extend more than 4-5 days into the past, it may not be possible to issue a carer cert online, and you may be advised to see your usual GP in person.

You can find more detailed information on backdated certificates HERE