1. to put an earlier date on a document than the actual date it was created or signed
2. to make something effective from an earlier date than when it was actually implemented

Examples

• The company backdates the contract to January 1st.
• She backdates her resignation letter to last week.
• The insurance policy backdates coverage to the purchase date.
• He backdates the check to avoid late fees.
• The new salary increase backdates to the beginning of the year.
• They backdated the agreement to include the previous quarter’s earnings.