Tip Calculator
Tip on the pre-tax amount or the total — decide first, because the difference compounds when you split.
Tip before or after tax
Tipping on the post-tax total gives a slightly larger tip. Neither is wrong — just be consistent when splitting.
Rounding up
Rounding the per-person amount up and keeping the difference is normal; it also makes the split exact.
Should I tip on takeaway?
Custom varies. In many places no, in the US yes.
How do I split unevenly?
Use the per-person figure as the base and adjust for who ordered what.