Weight-Based Medication Dose Calculator

Medication Dosing Guide

What's the key thing to understand about Paracetamol — The Safest Starting Point?

Paracetamol (acetaminophen) is the safest analgesic and antipyretic for most people including pregnant women, children, and the elderly. Adults: 500mg-1,000mg every 4-6 hours. Maximum 4,000mg (4g) in 24 hours. Overdose: paracetamol overdose is the leading cause of acute liver failure in the UK — often accidental (taking multiple products unknowingly containing paracetamol). Always check other medications (cold/flu remedies, codeine combinations) do not also contain paracetamol. Children (15mg/kg per dose, every 4-6 hours) should always be dosed by weight rather than age alone, since children of the same age can vary significantly in weight.

What should I know about Ibuprofen — Anti-Inflammatory?

Ibuprofen is an NSAID — anti-inflammatory, analgesic, and antipyretic. Adults: 200-400mg every 4-8 hours with food. Maximum 1,200mg/day (OTC limit). Prescription: up to 2,400mg/day. Children (over 3 months, over 5kg): 5-10mg/kg per dose, every 6-8 hours. Always give with food. Contraindications — do not use without medical advice: asthma (NSAID sensitivity in approximately 10% of asthmatics). Stomach ulcers or GI problems. Kidney disease. Heart disease or stroke history. Third trimester of pregnancy — ibuprofen and other NSAIDs should be avoided from this point onwards due to risks to the baby, with paracetamol being the safer choice throughout pregnancy generally.

What should I know about Never Use Aspirin in Children Under 16?

Aspirin is absolutely contraindicated in children and teenagers under 16 due to the risk of Reye's syndrome — a rare but potentially fatal condition causing liver and brain damage. This applies even to low-dose aspirin (75mg). If a child has fever, use paracetamol or ibuprofen. Aspirin in adults: low-dose aspirin (75mg daily) is prescribed as an antiplatelet drug for cardiovascular disease prevention. Standard-dose aspirin (300mg) is used acutely for suspected heart attacks. OTC aspirin (300mg): used for pain relief in adults, but never given to children or teenagers under 16 due to the risk of Reye's syndrome, a rare but serious condition linked to aspirin use in this age group.

When to Seek Medical Advice?

Seek medical advice before self-medicating if: fever in a child under 3 months. Fever lasting more than 3 days in children. Fever above 39.5°C unresponsive to medication. Any sign of serious illness (rash, difficulty breathing, confusion, severe headache). Pain not controlled by OTC doses. Regular need for pain relief (more than a few days per week). Any sign of overdose: nausea, vomiting, abdominal pain within 24 hours of high paracetamol dose — attend A&E immediately. The dose charts on medication packaging are a starting reference, not a substitute for checking with a pharmacist or GP if you're ever uncertain about dosing, especially for children or when combining medications.

What should I know about Weight-Based Dosing in Children?

Children's medication doses are calculated per kilogram of body weight rather than using a fixed adult dose scaled down by age, because body weight correlates much more closely with how a drug is distributed and processed than age does — two five-year-olds can differ in weight by several kilograms, and dosing by age alone would risk under- or over-dosing the smaller or larger child. This is why accurate, current weight (not an estimate, and not an outgrown weight from months ago) matters more for children's medicine than for adults, and why paediatric medicine labels and NHS dosing guidance (such as for paracetamol or ibuprofen) are structured as a dose per kilogram, or as weight-banded tables, rather than a single number. Children also metabolise many drugs differently from adults — sometimes faster, sometimes slower, depending on the drug and the child's age — so paediatric doses aren't simply 'adult dose divided by weight ratio' for every medicine. Always use the dosing information specific to the product and the child's current weight, and check with a pharmacist or GP for any medicine not explicitly labelled for children, or if the child has recently changed weight significantly.

What should I know about Checking for Duplicate Ingredients?

One of the most common causes of accidental medication overdose is taking two or more products that contain the same active ingredient without realising it — most often paracetamol, which is included not only in standalone paracetamol tablets but also in many combination cold, flu and sinus products, and some prescription painkillers such as co-codamol, which combines paracetamol with codeine. Taking a standard paracetamol dose on top of a "flu remedy" that already contains paracetamol can push someone over the maximum safe daily limit without them ever taking what looks like a double dose of any single product. The same risk applies to ibuprofen, which appears in some combination cold and flu products alongside other painkillers. It's worth checking the active ingredients list on every medicine packet — not just the brand name — before combining products, and never taking more than one product containing paracetamol at a time. This is particularly important when treating a child's illness, since parents may give a combination cough/cold medicine and a separate children's paracetamol without realising both already contain the same ingredient.

Weight-Based Dosing in Children: Why Age Alone Isn't Enough

Children's medication doses are calculated primarily by body weight (mg per kg) rather than age, because children of the same age can vary very widely in weight, and dosing by weight gives a far more accurate match to what a child's body can actually process. UK paracetamol and ibuprofen dosing charts are built around weight bands precisely for this reason, with age given only as a rough cross-check — a parent should always use the weight-based dose shown on the product label or NHS dosing chart when a child's actual weight is known, rather than defaulting to the age-based dose if the two disagree, and should never estimate a child's weight rather than actually weighing them when precision matters, such as for a smaller or lighter-than-average child. Liquid paediatric medicines also vary in strength between products (for example, children's paracetamol suspension commonly comes in 120mg/5ml and 250mg/5ml strengths), so the dose in millilitres is never interchangeable between products without re-checking the concentration on that specific bottle. Always use the measuring syringe or spoon supplied with the medicine, since a standard kitchen teaspoon is not a reliable 5ml measure and can lead to significant dosing errors in either direction.

Why Checking for Duplicate Active Ingredients Matters

Many combination cold and flu remedies already contain paracetamol as one of several active ingredients, and taking a separate paracetamol dose on top of one of these products — a common and easy mistake — risks exceeding the maximum safe daily dose without realising it, since the total isn't obvious unless every product's ingredient list is checked individually. The maximum adult paracetamol dose is 4g (4,000mg) in 24 hours from all sources combined, and exceeding this, even by a modest margin over several days, carries a real risk of liver damage; pharmacists specifically recommend checking the active ingredients list on every medicine taken together, not just the brand name, since very different-sounding products can share the same active ingredient.

Spacing Doses Correctly Through the Day

Paracetamol doses should generally be spaced at least 4-6 hours apart, with a maximum of 4 doses in 24 hours for adults; ibuprofen doses are typically spaced 6-8 hours apart with a maximum of 3 doses in 24 hours. Paracetamol and ibuprofen can be alternated or taken together if needed (they work via different mechanisms and don't compound the same organ-specific risks in the way doubling up on paracetamol does), which is sometimes recommended by a GP or pharmacist for fever that isn't responding to one medicine alone, but this should be done following specific dosing instructions rather than improvised, particularly for children.

Why Expiry Dates on Medicines Matter

Taking medicine past its printed expiry date isn't typically acutely dangerous for most tablets stored correctly, but potency can decline meaningfully after expiry, meaning the dose taken may deliver less active ingredient than intended — this matters most for medicines where getting a full, accurately-dosed effect is important, such as treating a fever or significant pain, and liquid formulations and anything requiring refrigeration degrade faster than tablets once past their stated shelf life.

Why 'Natural' or Over-the-Counter Doesn't Mean Risk-Free

Over-the-counter status reflects an established safety profile at the stated dose for the general population, not an absence of risk at any dose or in any individual — herbal and supplement products can also interact meaningfully with prescribed medicines (St John's Wort and many antidepressants or contraceptives being a well-documented example), so checking with a pharmacist before combining any new over-the-counter or herbal product with an existing prescription remains sound practice even for products marketed as gentle or natural.