Co-Author Royalty Split Calculator
Enter a royalty payment, each partner's share and any expenses they paid. The calculator repays expenses first, then splits the rest.
How the split works
repaid to a partner = min(payment, total expenses) × their expenses ÷ total expenses
left to split = payment − total expenses (if positive)
partner's share = left to split × their share ÷ all sharesExpenses come off the top. If one payment doesn't cover them all, each partner gets back the same fraction of what they paid, and what is still owed carries into the next payment. Once expenses are repaid in full, enter 0 for them and every later payment is split straight by percentage.
Worked example: two co-authors
Two authors share a series 50/50. Partner 1 paid $300 for the cover and Partner 2 paid $100 for proofreading. The first month's royalty is $1,000:
- $400 of expenses are repaid first: $300 and $100.
- The remaining $600.00 is split 50/50, $300.00 each.
- Partner 1 receives $600.00 and Partner 2 $400.00.
If the first payment had been only $200, it would cover half the expenses: Partner 1 gets $150.00, Partner 2 gets $50.00, and $200.00 is still owed from the next payment.
Worked example: author and illustrator
A picture book's author and illustrator agreed 60/40 with no shared costs. A month's royalty of $842.50 splits into $505.50 and $337.00. Splits that don't divide evenly round to the cent: three partners on 40/40/20 of $1,234.56 get $493.82, $493.82, $246.91, one cent short of the total. Agree in advance who absorbs rounding differences, usually the account holder.
Put the agreement in writing
A short written agreement prevents most co-author disputes. It should name who holds the KDP account and receives payments, the percentages, which expenses are repaid first and up to what limit, how often money is passed on after KDP pays, who decides on price changes and ads, and what happens if one partner wants to leave or the book goes out of print. Keep a simple ledger of each payment with this calculator's numbers so both sides can check it. To see when the shared costs will be earned back, use the break-even calculator.
Frequently asked questions
Does KDP split royalties between co-authors?
No. KDP pays all royalties for a book to the one account that published it. The account holder then pays the others, so agree the split in writing before publishing, including who holds the account and when payments go out.
Should expenses be repaid before the split?
It is the most common fair arrangement when one person paid more of the upfront costs, such as cover, editing or ads. The calculator repays them first and splits only what is left. If you agreed instead that costs are shared by the same percentages, enter 0 expenses and reduce the total by the costs.
What if the shares don't add up to 100%?
The calculator uses each share as a proportion of the total shares, so 2 and 1 work the same as 66.7% and 33.3%. It warns you when percentages don't add to 100, in case that was a typo.
How should ads be handled?
Either treat ad spend as an expense to be repaid to whoever paid it, or agree that each partner funds ads in proportion to their share. Repaying first is simpler to track month by month.
Guides that use this calculator
Related tools
- KDP Printing Cost CalculatorPrint cost per copy for every ink, trim and marketplace
- KDP Paperback Royalty CalculatorRoyalty per copy, minimum price and price for a target royalty
- KDP Hardcover Royalty CalculatorHardcover printing cost, royalty and minimum price
- Book Break-Even CalculatorCopies and months to earn back cover, editing and ad costs