The number of days an affiliate can earn commission on a conversion (sale or lead) by a referred visitor.
If an affiliate program offers 45 return days, commissions are earned for conversions completed any time within 45 days of the initial click-through on the affiliate link. The visitor may later go directly to the merchant’s site and not visit the affiliate’s site again, as software is used to track the visitor’s origin.
If an affiliate program offers zero return days, commissions will only be earned for conversions completed on the initial visit following a click-through. Once the visitor leaves the destination site, the commission opportunity is lost, even if the visitor returns in a few minutes to complete a transaction.
Affiliate programs vary as to which affiliate gets credit for a sale when a visitor has followed more than one affiliate links prior to the sale; some programs favor the first affiliate, some programs favor the last affiliate.
The Affiliate Cookie Fortune
ClickZ (July 27, 2001)