Split bills fairly calculator: equal, income and use side by side

What does a fair split mean?

A fair split depends on the question the group asks, and each question gives a different number. Equal asks who is in. Income asks who can afford more. Use asks who used the thing more. The calculator puts all three side by side so the group can see how far apart they are before anyone argues for one.

A rule works best when everyone agrees to it before the bill arrives. The calculator shows what each candidate costs each person, so the agreement is made with the numbers in front of you.

How does the calculator work?

A person is in the split when their income or their use is above 0.

1. Equal. The bill divided by the number of people in the split.
2. By income. The bill times the person’s income, divided by everyone’s income added together.
3. By use. The bill times the person’s use, divided by everyone’s use added together.
4. Average of the three. Add a person’s three shares and divide by 3.

The top line shows the biggest gap: for the person whose share moves most between rules, the highest of their three shares minus the lowest. Shares are in whole cents and each rule adds up to the bill exactly.

Use the same period for every income, such as monthly take-home pay. Use one unit for every use figure, such as days at home, kWh, miles or orders.

Worked example: a $900 bill for three

Say three people split a shared $900 bill. Their monthly incomes are $2,000, $3,000 and $5,000, and in the month they were at home for 24, 18 and 6 days. These are the numbers the calculator opens with.

• Equal: $900 ÷ 3 = $300 each.
• By income: the incomes add up to $10,000, so the shares are 20%, 30% and 50%.
• By use: the days add up to 48, so the shares are 50%, 37.5% and 12.5%.
• Average for person 1: ($300 + $180 + $450) ÷ 3 = $310.

Rule	Person 1	Person 2	Person 3
Equal	$300	$300	$300
By income	$180	$270	$450
By use	$450	$337.50	$112.50
Average of the three	$310	$302.50	$287.50

Person 3 pays $112.50 by use and $450 by income, so the biggest gap is $337.50. By income, every person puts the same 9% of their own income toward the bill: $180, $270 and $450 are each 9% of $2,000, $3,000 and $5,000. The average pulls everyone toward the middle, and the shares still add up to $900.

When does each rule fit?

• Equal fits when everyone is in and uses and earns about the same. It has the fewest numbers to argue about.
• By income fits a cost that does not change with use, such as rent or an internet plan, when incomes differ a lot. It is a proportional split, and the income-based split calculator goes deeper on it.
• By use fits when people use the thing in clearly different amounts and you can count it. If you already know the ratio, the split by shares calculator takes it directly.
• The average fits when two people argue for different rules. It takes a third of each and is a compromise, not a ruling.

Mistakes to avoid

• Mixing periods. A yearly income next to a monthly one makes the yearly person count twelve times as much.
• Mixing units. Days for one person and hours for another make the use shares meaningless.
• Leaving a slot half filled. A person with income but no use pays nothing by use. Fill both boxes, or leave both at 0 for someone who is not in the split.
• Treating the result as a verdict. The calculator shows what each rule costs. Whether the group chooses equal, income, use or the average is the group’s call. For couples, should couples split bills 50/50 covers that decision.

Using the numbers in EvenOut

In EvenOut the split method is chosen for each expense, so one group can use a different rule for each bill. Choose “Equally” for an equal split, “Percent” and type 20, 30 and 50 for the income split, or “Shares” and type 4, 3 and 1 for the use split, which is 24, 18 and 6 reduced. With Percent or Shares, each person’s dollar share shows under their name before you save. The formulas for splitting bills lays out every method side by side.