The answer box at the top

The big line is a school morning, not a number of hours: the weekday, the date and your school’s first bell. Under it, the “Set by” line names the one event that decided it and the moment its wait ends, so you can check the arithmetic yourself before you pack the backpack.

Until you change anything, the box shows an example. As soon as you answer a question, it switches to your child’s times. If a question is still open, the date carries a “Preliminary” tag that names what is missing.

Six short questions

Fever, fever reducer, getting better, vomiting or diarrhea, an antibiotic for strep throat or pink eye, and warning signs, where “None of these” has to be ticked before the date stops being preliminary. You can jump between them in any order with the numbered tabs, and the answer box updates after every tap.

Each time question has quick answers like “Last night” or “This morning.” A quick answer counts the latest moment it could mean: “Last night” counts as midnight, “This morning” as noon or the current time, whichever is earlier. The line under the fields shows exactly what was counted, and the date and time fields let you put in the real time instead.

Why the fever reducer has its own clock

School rules say fever-free for 24 hours without fever-reducing medicine. Acetaminophen or ibuprofen can hide a fever that would otherwise still be there, so the calculator runs a second 24-hour clock from the last dose, next to the clock from the last fever. It asks only when the last dose was given, never how much.

Here is how that plays out. A last fever at 7:00 AM on Monday clears at 7:00 AM on Tuesday, in time for an 8:00 AM bell, so the answer is Tuesday. Add a dose of ibuprofen at 9:00 PM on Monday and the medicine clock runs until 9:00 PM on Tuesday, so the answer becomes Wednesday. The “What changed” line under the answer says this in one sentence whenever an answer moves the date.

What holds the date

Every rule that applies gets a row: no fever, no fever reducer, symptoms getting better, no vomiting or diarrhea, time on the antibiotic. Rows that are finished turn grey and say “Done.” The row that ends last is marked “This one decides.” A row that cannot start yet, for example while the fever is still there, says what it is waiting for, and there is no date until it starts.

The school week

The ribbons show the same clocks on a calendar. Each one starts at its event and ends when its wait is over. Days without school are hatched, dotted lines mark the first bell, and the green marker sits on the first bell after the last ribbon ends.

A clock that ends at 10:00 AM does not send a child in mid-morning. The return is always the start of a school day, so weekends, holidays and teacher days you add are skipped.

Your school’s rules

The fever and getting-better defaults follow CDC: 24 hours without fever or fever reducer, and 24 hours with symptoms getting better. The 24 hours after the last vomiting or diarrhea and the wait on an antibiotic come from common school policies, not from one CDC rule. Some schools ask for 48 hours, a longer wait after two or more episodes, 12 or 24 hours on an antibiotic, or one full school day at home without symptoms. Each of these is a switch in the rules panel, along with the first bell time, the school days and the days without school.

If your school’s written policy says something different from the defaults, its rule is the one that counts. The American Academy of Pediatrics guidance for child care is looser than most school policies on fever, and the calculator follows the school.

Where the calculator stops

A rash with a fever, blood in the stool, trouble breathing, a baby under 3 months with any fever, or a diagnosis with its own return rule such as chickenpox or measles turns off the date. For those, your child’s doctor or the school nurse decides. The calculator does not decide whether a child is still contagious; after going back, CDC suggests five more days of extra care around other people.

Sources: CDC, Preventing Spread of Respiratory Viruses When You’re Sick; AAP exclusion criteria for child care and schools; school health policies such as Pinellas County Schools and Shawnee Mission School District. This calculator applies the rules you choose to the times you enter. It is not medical advice.