Paediatric Calculators
Paediatric calculators, with safety front and centre
Weight-based tools with prominent cautions, transparent formulas and named clinical review — for learning and quick reference.
Higher-risk — read first. Paediatric calculations are weight-based; small errors can cause serious harm. For education and reference only. Always independently verify every result against local paediatric guidance and the BNF for Children, and use a second checker, before any clinical use. Values are not stored.
Maintenance fluids (Holliday-Segar)
Estimates 24-hour maintenance fluid for a child by weight. A starting estimate only — adjust for clinical status and local policy.
Method: Holliday-Segar (100/50/20 mL/kg/day). Last reviewed June 2026.
Calculator library
More paediatric tools
Maintenance fluids (Holliday-Segar)
APGAR score
Weight-for-age centile
Paediatric GCS
Estimated weight (APLS)
Corrected gestational age
Why paediatrics is different
Small bodies, smaller margins for error
Almost everything in paediatric calculation scales with weight, and children span an enormous range — from a preterm neonate of well under a kilogram to an adolescent approaching adult size. Because doses, fluid volumes and physiological norms all shift with that weight and age, the same input error produces a far larger proportional effect than it would in an adult. A misplaced decimal point or a weight entered in the wrong units can translate into a tenfold discrepancy. That is why these tools lead with a safety caution and why we ask you to use a second checker for anything that touches a real patient.
The maintenance-fluid calculator above demonstrates the Holliday-Segar method, the standard approach to estimating a child's 24-hour maintenance requirement: 100 mL/kg/day for the first 10 kg, 50 mL/kg/day for the next 10 kg, and 20 mL/kg/day for each kilogram beyond 20 kg. It returns both a daily volume and an hourly rate. Crucially, it is a starting estimate. Real prescribing must account for the clinical picture — dehydration, fever, ongoing losses, cardiac or renal status — and follow local fluid policy and the BNF for Children.
Safe practice with these tools
A short checklist before you rely on any result
- Confirm the child's weight is accurate, recent and entered in kilograms.
- Re-read the formula and the assumptions the calculator states.
- Treat the output as an estimate to be adjusted for clinical status.
- Cross-check against the BNF for Children and your local paediatric guidance.
- Have a second competent person independently verify the figure before clinical use.
The wider paediatric set
Alongside maintenance fluids, we are building out tools for the APGAR score, weight-for-age centiles, paediatric GCS, APLS estimated weight and corrected gestational age — each with the same transparency and cautions. For adult scores and conversions, see the adult calculators, and browse everything computed so far in the calculator library. When a calculation points to a medicine, confirm its details in the Medicine Finder and the Drug Safety & Side-Effect Checker.
Education and reference only. Nothing on this page is a substitute for clinical judgement, local paediatric policy or the BNF for Children. Independent double-checking is essential before any paediatric calculation is acted on.
Answers
Frequently asked questions
Why are paediatric tools higher-risk?
Paediatric dosing and fluids are weight-based and small errors can cause significant harm. These tools are education and reference only — always double-check every result against local paediatric guidance, the BNF for Children and a second checker before any clinical use.
Where do the formulas come from?
Each calculator shows its formula and references and a last-reviewed date. The maintenance-fluid tool uses the Holliday-Segar method. Results are computed in your browser and not stored.
Who reviews these tools?
Reviewed by our Clinical Director. See our Quality & Editorial Policy.
How is the maintenance-fluid estimate calculated?
It uses the Holliday-Segar method: 100 mL/kg/day for the first 10 kg of body weight, 50 mL/kg/day for the next 10 kg, and 20 mL/kg/day for each kilogram above 20 kg. The result is shown as both a daily volume and an hourly rate, and is a starting estimate to be adjusted for the child's clinical state and local policy.
Can I use the adult calculators for an older child?
No. Even in older children, paediatric thresholds, dosing and fluid requirements differ from adult ones. Use these paediatric tools and the BNF for Children, not the adult calculators.
Need a custom paediatric tool?
We build evidence-led, safety-reviewed calculators for teams.