An online system receives a discount offer from a merchant and displays the offer to a user before the offer's start time. The online system also defines one or more triggering conditions and sends a notification to remind the user about the discount offer when a triggering condition is satisfied. One of the triggering conditions can be based on whether the user has accessed a web page provided by the merchant. The merchant system provides a web page that sends an indication to the online system when the user accesses the web page. After receiving the indication, the online system sends a notification about the discount offer to the user. Sending the notification in this manner has the effect of reminding the user of the discount offer after the user has already expressed an interest in the merchant and its products by viewing the merchant web page.