Your family, your in-laws, one Thanksgiving and one Christmas. Enter who is involved and which holidays you share out. You get a plan for the next few years, a count per family, and a link you can send to both sides.
A list of years can look balanced and still hand one side more Christmases. Under the grid, the count table adds up every holiday per family: how many Thanksgivings, Christmas Eves and Christmas Days each one gets over the whole span, and the total.
If the numbers differ, the table says by how much. That usually means the plan stops in the middle of a cycle, so adding or dropping a year fixes it. Show both sides the counts before anyone argues about the dates.
Each holiday moves to the next family every year, in the order you list them. The four rotations differ in where each holiday starts. With "Swap everything", one family has all of them and the other has none that year. With "Mix them up", the family that has Thanksgiving does not also have Christmas Eve.
The count table shows what each family gets of each holiday. A holiday visits every family once per cycle, which is 2 years for two families and 3 for three. Any span that is a whole number of cycles comes out even. A span that stops mid-cycle shows a warning with the difference.
Thanksgiving is the fourth Thursday of November, the US date. The page does not know about Canadian or other dates, and it does not know about your travel, kids or work shifts. It is a starting point for a conversation, and you can change the start year or the order of the names until the first year suits both sides.
Nothing is saved on the server. The plan is the web address, so sending the link sends the plan, and anyone who opens it can change it for themselves. To keep it, print it or save the link.
New to the topic? Read how to split holidays between two families for the common patterns, or alternating Christmas years with in-laws for the yearly swap. Ready to share it? See how to tell your parents you're alternating holidays.