Tinker 
How to use it
Type the bill total, the tip percentage you want to leave and how many people are sharing. Results update instantly. Tick the rounding box if you would rather everyone pays a whole amount; the small extra is added to the tip.
The formula
Tip = bill × tip % ÷ 100. Total = bill + tip. Each share = total ÷ number of people. When rounding is on, each share is rounded up to the next whole unit, the total becomes share × people, and the tip is the total minus the bill. The effective tip shows what percentage you actually left after rounding.
Worked example
Three friends have a $64.50 bill and want to tip 20%. The tip is 64.50 × 0.20 = $12.90, so the total is $77.40 and each pays $25.80. With rounding on, each pays $26, the total is $78 and the tip becomes $13.50, an effective tip of about 20.9%.
Practical tips
Customs differ: tipping norms vary widely by country and type of service, and some bills already include a service charge, so check the receipt before adding more. Decide whether to tip on the amount before or after sales tax and enter that figure as the bill.
Frequently asked questions
Should I tip on the pre-tax or post-tax amount?
Either is common. Tipping on the pre-tax amount is slightly cheaper; enter whichever figure you prefer as the bill.
How do I quickly work out 15% or 20% in my head?
Find 10% by moving the decimal one place left. Double it for 20%, or add half of it for 15%.
Does this work with any currency?
Yes. The maths is the same for any currency; just ignore the $ symbol.
What if people ordered different amounts?
This tool splits evenly. For uneven orders, run it once per person using their own subtotal as the bill and 1 person.