This advice is subtly no longer correct in delivery apps, as they have creative ways of calculating tip. The correct advice is probably to double the tax. So i

This advice is subtly no longer correct in delivery apps, as they have creative ways of calculating tip. The correct advice is probably to double the tax. So it used to be, you would order something for delivery, they would charge you the in-person price for each item, add them up, subtract discounts, and give you a number called the “subtotal.” To this they would add a delivery fee, taxes, and you would add your tip as 15% of subtotal. In the dark pattern world that we find ourselves, the menu items on a typical delivery app are secretly priced 25% higher than in-person. (Go ahead, look up Applebees’ “2 for $28” menu item on a delivery app, tell me it doesn't cost $35.) This is so that they can advertise “Reduced delivery and service fees if you subscribe to our monthly service so that we can get MRR from forgetful people!!”. Then the tax and service fees are added to the cart total, but the discount is NOT subtracted, before they provide helpful tip buttons. Doordash doesn't even tell you the percentage, they just expect you to pick the smallest one and it's a 30 or 40% tip or whatever, Uber will tell you “oh you’re only giving this person a 10% tip you monster” even though it's a 15% tip calculated the “hard way.” It all adds up, picking up a big nice breakfast in bed for me and the kid and my wife on my wife's birthday from Starbucks was like $30 via the Starbucks app, I punched it into Uber Eats and they wanted to charge me almost double for the identical order. So if that ~180% had a 15% tip in it, then it was actually ~57% marked up to begin with and you actually paid a 24% tip. (I don't know if that's typical of Uber Eats but it suggests that on Uber Eats you should only tip what-they-call-10%.) But they will be unlikely to play these games with the tax man, so “double the tax” is probably slightly safer?