Hello smckay,

The markup feature in QuickBooks Online is used only with billable expenses on the vendor side.  So when you have billable time or charges that you pass on to the customer - you're able to set a markup for when you invoice that customer.

Right now, there's no option to add a Markup column on estimates for QuickBooks Online. You may send a product suggestion through this link: http://feedback.qbo.intuit.com. This will make our product developer team aware of how you want the program to work. We'd really appreciate your suggestion since most of our features come from our customers.

Please let me know if there's anything else that you need help with.