When can I take the next dose?

How it works

You copy two numbers from your medicine's label: the shortest gap between doses, and the most in 24 hours (in doses, or in tablets or mL). The timer does the arithmetic and nothing else. It doesn't know the right dose for anyone, whether a dose is needed, or what else someone takes.

The gap is counted from when the last dose was actually given, as Tylenol's dosing advice says. If a label gives a range, like every 6 to 8 hours, enter the first number: that's our reading of a range as its shortest gap.

The 24-hour count covers the 24 hours before now, so a dose stops counting exactly a day after it was given. Labels say "in 24 hours" or "a day"; we count both the same way: any 24 hours, not since midnight. That counts at least as many doses as a calendar day would, except on the day the clocks go back and a day is 25 hours long. Hours are real hours, so a night when the clocks change is still 24 hours.

We don't offer ready-made medicines: labels differ by product, strength, age, weight and country. Two medicines with the same ingredient get a note, because FDA advises against taking more than one medicine containing acetaminophen. Each card counts only its own doses.

The timer never suggests alternating medicines. For a child with a fever, the NHS says "do not alternate ibuprofen and paracetamol, unless a health professional such as a doctor or nurse tells you to", and then "it can help to write down when you gave each medicine". NICE guideline NG143 says "do not give both agents simultaneously" and to "only consider alternating these agents if the distress persists or recurs before the next dose is due". If a professional has told you to alternate, give each medicine its own card: each keeps its own gap and count.

Everything you save stays on this device, and your medicines and doses are never put in a link (an example link in one of our articles can fill in the form, but it saves nothing). To hand over a night shift, use "Copy as text". If too much was taken, call Poison Control (1-800-222-1222) in the US or NHS 111 in the UK.

Questions people ask

How long should I wait between doses?

As long as your medicine's label says: it gives the gap, such as "every 4 hours" or "every 6 to 8 hours". Tylenol's FAQ reads its gap as "no sooner than every 4 hours after the last dose"; this timer uses the shortest gap you enter and counts it from when the last dose was actually taken.

Can I alternate acetaminophen and ibuprofen?

For a child with a fever, the NHS says not to alternate them unless a doctor or nurse tells you to. NICE, writing about fever in children under 5, advises not giving both at the same time, and considering alternating only if the child's distress persists or comes back before the next dose is due. If you've been told to alternate, add each medicine on its own card: each keeps its own gap and 24-hour count.

How does it count "in 24 hours"?

This timer counts any 24-hour stretch, not since midnight, and shows when the oldest dose stops counting. Reading "a day" that way is ours; it counts at least as many doses as counting from midnight would, except on the day the clocks go back and a day is 25 hours long.

What if a dose was given twice by mistake?

In the US, call Poison Control at 1-800-222-1222; it's free and confidential. In the UK, call NHS 111. The Tylenol Extra Strength label says quick medical attention is critical even if you notice no signs or symptoms, and Poison Control says to call 911 if someone collapses, has a seizure, has trouble breathing or can't be woken.

Why doesn't it suggest a dose?

Because the right numbers depend on the product, its strength, and the person's age and weight. Three Tylenol products alone give gaps of 4 to 6, 6 and 8 hours, and Infants' Motrin holds twice the ibuprofen per mL of Children's Motrin. Copy the numbers from your own label.

Sources

1. FDA: 21 CFR 201.66, the Drug Facts label (Directions)
2. DailyMed: Tylenol Extra Strength Drug Facts (directions and overdose warning)
3. DailyMed: Tylenol Regular Strength Drug Facts
4. DailyMed: Tylenol 8 HR Arthritis Pain Drug Facts
5. DailyMed: Children's Motrin Drug Facts
6. DailyMed: Infants' Motrin Drug Facts
7. FDA: questions and answers on the change to one infant acetaminophen concentration
8. FDA: don't overuse acetaminophen
9. Tylenol: frequently asked questions (gap counted from the last dose)
10. NHS: fever in children
11. NHS: ibuprofen for children
12. NHS: paracetamol for children
13. NICE NG143: fever in under 5s, recommendations 1.6
14. AAP (Sullivan and Farrar 2011): fever and antipyretic use in children
15. Cochrane 2013: alternating and combined antipyretics for fever in children
16. Poison Control: medication errors and double dosing
17. Poison Control (poison.org)