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LunchMath™ FAQ

This FAQ section should address most of the questions you have. For additional support, you may email us at

  • Q: What is the minimum information I must enter to use LunchMath?
    A: You only need to enter values in the Total and the number of people (Num. People) fields. LunchMath defaults to a 15% tip when you start the program. LunchMath will display the Per Person amounts rounded up to the nearest 25 cents based on these values. Entering the Subtotal allows LunchMath to base the tip on the Subtotal which is the accepted method of calculation.
  • Q: Why does LunchMath always round up to the nearest 25 cents?
    A: The LunchMath tip calculation engine is designed to ensure that the numbers stay positive when Round is On. If LunchMath rounded down as well as up, then it would be possible to get negative numbers when the tip percentage was set to small values. This is why LunchMath rounds up.
  • Q: Why is a Tip value displayed even though I've set the tip percentage to 0?
    A: If the amounts are not evenly divisible by the number of people splitting the bill, the amount left over during splitting will be displayed in the Tip field.
  • Q: Why is the value in the Chng field red?
    A: The Chng value shows how much change a person should get back after putting in their money. If someone puts in less money than they owe for their portion of the bill, LunchMath shows a minus sign (-) and turns the value red to indicate that the person will need to borrow money. The amount shown in the Chng field is the amount of money that person needs to borrow to pay their portion of the bill.
  • Q: Why doesn't LunchMath allow me to enter the tax rate directly?
    A: Many locales have different tax rates for food and alcohol and the rates are rarely on the bill. If you enter a subtotal, LunchMath will use that and the total to calculate the average tax rate. LunchMath will use that tax rate to calculate the Pay amount for any adjusted values.
  • Q: What is the Who field for?
    A: The Who field is strictly a comment field to help you remember which person an adjustment is for. It is an optional field and has no effect on any calculation.
  • Q: What do I do if I have a discount? I want to make sure the server gets their tip based on the pre-discounted total.
    A: If you enter the Subtotal before the discount is applied and the Total after the discount is applied, LunchMath will calculate the tip based on the Subtotal splitting the tip across all of the people in the party. If you would like to give the entire discount to one person, enter the Subtotal, Total, and put the amount of the discount in the Adjust field. The person receiving the discount should pay the amount in the Pay field while everyone else will pay the amount in the Rest Owes field.


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