Children's Antihistamine Dose Calculator (Cetirizine, Loratadine, Fexofenadine, Diphenhydramine)
Find the label dose of children's cetirizine, loratadine, fexofenadine or diphenhydramine liquid by age: mL and mg per dose, how often and the 24-hour maximum, following the OTC product labels.
How it works
dose = the OTC label dose for the child's age band (these labels are age-based, not weight-based) · mg = mL × product strength (e.g. 1 mg/mL cetirizine; 5 mg/5 mL loratadine; 30 mg/5 mL fexofenadine; 12.5 mg/5 mL diphenhydramine)
Children's allergy medicines sold over the counter are dosed by age on the product label. Cetirizine and loratadine are given once a day, fexofenadine twice a day, and diphenhydramine (a sedating, older antihistamine) every 4–6 hours with a maximum of 6 doses a day. Under 2 years none of them has an OTC dose, and diphenhydramine should not be used under 6 without a doctor. Check the strength on your bottle — tablets, chewables and "infant" products differ — and use the dosing device that comes with it.
Worked example
A 4-year-old with hay fever, children's cetirizine 1 mg/mL: the label dose for ages 2–5 is 2.5 mL (2.5 mg) once daily, which may be increased to 5 mL once daily (or 2.5 mL every 12 hours); never more than 5 mL (5 mg) in 24 hours. At age 6 the dose becomes 5–10 mL once daily.
Sources: DailyMed: children's cetirizine oral solution label · DailyMed: children's loratadine oral solution label · HealthyChildren.org (AAP): diphenhydramine dosage table
Frequently asked questions
How much cetirizine can I give my child?
By the children's Zyrtec label: ages 2–5, 2.5 mL (2.5 mg) once daily, up to 5 mL a day; ages 6 and over, 5–10 mL (5–10 mg) once daily, maximum 10 mL in 24 hours. Under 2, ask a doctor.
What is the loratadine dose for children?
Children's loratadine 5 mg/5 mL: ages 2–5, 5 mL once daily; ages 6 and over, 10 mL once daily. Do not give more than one dose in 24 hours.
Can I give Benadryl to a toddler?
Not without a doctor's advice. The label says do not use under 2 years and do not use at 2–5 years unless directed by a doctor. Diphenhydramine can cause dangerous over-sedation or agitation in young children.
Why does the label dose by age instead of weight?
OTC labels are written for typical children in each age group so parents can dose without weighing. Doctors sometimes prescribe weight-based doses for very small or large children — follow their instructions if so.
Related calculators
Educational calculation only, not medical advice. Always follow the label of the exact product you have and your child's doctor or pharmacist; use the dosing syringe or cup that comes with the medicine, never a kitchen spoon. Call your local poison control center if you think too much was given.