decided on the percentage tip you want to leave, calculate your tip based on the total before tax. Also check and see if there's a service charge, in which case you should not leave any additional tip (unless you had an exceptional experience with the staff).
If you've ordered a lot of alcoholic drinks, you might want to calculate your tip on your food separately from your drinks. You can tip at a lower rate for drinks, usually at around 10 to 15 percent, rather than the 15 to 20 percent that is usual for food. If you've used any coupons or discounts, calculate your tip based on how much you would have paid without those discounts. Tipping can be confusing and varies. But a general rule for waiters is to tip 15 to 20 percent of the pre-tax bill, and $2 to $5 per night for housekeeping service.