Keeping a Fever Diary for Your Child: 7 Mistakes Almost Every Parent Makes

The GP asks: "When did the temperature start, and how high was it last night?" You have been checking for three days — and standing in the room, you realise you cannot give a single reliable number.

Here is the short version: this is not your memory failing. It is that the details that make a reading useful are usually not written down with it — the time, the thermometer, the medicine.

Which seven details those are, and how to capture them from your next reading onwards, is below section by section.

What should go into a fever diary?

Five things belong next to every reading: the date and time, the temperature itself, which thermometer you used and where, any medicine with the dose and the time you gave it, and one short note on how your child seemed. That combination is what turns separate numbers into a picture someone else can read.

For context on the numbers: a normal temperature in babies and children is about 36.4C, though this varies slightly. A high temperature or fever is usually considered to be 38C or above. In most children the temperature returns to normal within 1 to 4 days.

The NHS also asks you to check on your child regularly, including through the night. Those night-time readings are exactly the ones that go missing by morning if nothing is written down.

Which signs need help straight away?

Some signs matter more than any number in a diary. They are not something to note and watch — they need help immediately, whatever the thermometer says. Breathing, responsiveness and rashes are the three to watch most closely.

Separate from that, call 111 if your child is under 3 months with a temperature of 38C or higher, is 3 to 6 months with a temperature of 39C or higher, has had a high temperature for 5 days or more, has a rash alongside the fever, shows signs of dehydration, or simply refuses food and seems unwell to you. If none of that applies and your child is drinking, responding and can be comforted, then watching and writing things down is exactly the right thing to do.

What do parents usually get wrong in a fever diary?

The common mistakes are not about the number itself but about its context: no time recorded, a different thermometer each time, an awkward moment to measure, medicines noted from memory. Each one turns a solid piece of information into a guess — and guesses do not help in the consulting room.

Mistake 1: Recording the number without the time

"38.9" on its own says very little. What a GP is looking for is the direction of travel — rising, falling or holding steady — and that only exists if each reading is anchored to a clock time. It also matters for medicines, because doses have to be spaced evenly, and you cannot space anything evenly against a number with no time on it.

Mistake 2: Changing thermometer or site between readings

Ear in the morning, forehead at lunchtime, armpit at bedtime — and now you have three readings that cannot be compared with each other. Always use the thermometer in the armpit with children under 5 years, and use a digital thermometer for a fast, accurate reading. Pick one method and stay with it for the whole illness.

Mistake 3: Measuring at the wrong moment

Your child's temperature can be higher than usual if they have been wrapped up tightly in a blanket, are in a very warm room, have been very active, are cuddling a hot water bottle, are wearing a lot of clothes, or have just had a bath. None of those readings are wrong exactly — they just are not comparable to the others. Let your child settle for a few minutes first, and if you did measure straight after a bath, note that too.

Mistake 4: Logging medicines without the dose and the time

This is the mistake with the biggest consequences. With paracetamol you should wait at least 4 hours between each dose and give no more than 4 doses in 24 hours, and the amount depends on your child's age. The NHS puts it plainly: it can help to write down when you gave each medicine, to make sure the doses are spaced evenly and to avoid giving too much. If an extra dose does happen, our guide on a double dose given by accident walks through what to do. And on which medicine to reach for, see ibuprofen or paracetamol.

Mistake 5: Recording only the temperature

The number is not the whole story. Give paracetamol or ibuprofen if your child is distressed by the fever — not because the thermometer crossed a line. What the GP wants alongside the reading is how your child actually was: did they drink, did they respond, did they sleep? One short note per reading is enough.

Mistake 6: Not pinning down when it started

"When did it start?" is the first question you will be asked, and the hardest one to answer looking back. After three broken nights the days blur together. Record the first unusual reading with its date, and the answer is simply there later on. That five-day mark for calling 111 only means something if you know which day was day one.

Mistake 7: Relying on a scrap of paper and your memory

At three in the morning the notepad on the bedside table is the problem, not the tool. It is in the other room, the pen has vanished, and by morning nobody knows whether that reading was from 2am or 4am. And if two adults are taking turns, an entry only one of them can see is how gaps — and double doses — appear in the first place.

How often should you check your child's temperature?

Often enough to see a trend, and at roughly the same times each day. The NHS asks you to check on your child regularly, including through the night. More readings do not produce a clearer picture; readings you can line up against each other do.

A simple rhythm works well: once in the morning, once in the afternoon, once in the evening, plus any time your child's condition noticeably changes. Alongside that, give them plenty of fluids and keep breastfeeding if you are, look out for signs of dehydration, and keep them at home while they are unwell.

There are also a few things not to do. Do not undress your child or sponge them down to cool them, do not cover them in too many clothes or bedclothes, and do not give aspirin to children under 16.

How do your notes become something a GP can actually read?

By giving every reading the same four fields — time, temperature, method, one-line note — plus every dose of medicine with the amount and the time. Twenty entries like that make a curve. Twenty numbers spread across scraps of paper make nothing.

That is what Mona is built for. You tap in the time and temperature in a few seconds, the medicine log holds the dose and the exact time it was given, and the fever chart shows the whole course of the illness rather than isolated moments. Whoever gets up in the night makes the entry, and the other one sees it in the morning without anybody having to remember to mention it.

Your GP will ask: when did it start, how high did it get in the evening, when did your child last have which medicine and how much, and have they been drinking? If you have been writing things down, those four answers are already there. Why they are so hard to produce on the spot is the subject of our article on why your memory fails at the GP.

Common questions about fever diaries

At what temperature should I start writing things down?

Start at the first reading that looks unusual to you, even below 38C. The start date is the detail most often needed later and most often misremembered, and a single entry with a date and time is enough to secure it. Everything after that is easier.

Do I need to wake my child at night to check?

The NHS asks you to check on your child regularly, including through the night, so some night-time checks are expected. In practice, check when your child is stirring anyway or when something changes. Whatever you do, write the time down then and there — those are the readings that vanish by morning.

Which thermometer should I use for my child?

Use a digital thermometer, which you can buy from pharmacies and supermarkets, and place it inside the top of the armpit with the arm gently closed over it. Always use the thermometer in the armpit with children under 5 years. Consistency matters more than the brand.

How long should I keep the diary going?

Until the temperature has settled and your child is eating, drinking and playing normally again, plus a day or two beyond that. A temperature that climbs again after a clear day is exactly the kind of pattern that matters clinically and is easily lost without notes.

Is it enough to note the highest reading of the day?

No. A daily maximum hides the thing that matters most: whether the temperature is climbing, falling or holding, and how it responds to medicine. Two children with the same peak reading can be having completely different illnesses.

What if I forgot to take a reading?

Do not fill the gap with a guess. A missing entry is harmless; an invented one can send an assessment in the wrong direction. Just record the next reading in full and carry on.

Summary: watch, call 111, or call 999?

Situation	What to do
Stiff neck, rash that does not fade, breathing difficulty, first fit, drowsy and hard to wake	Call 999
Under 3 months with 38C or above, or 3 to 6 months with 39C or above	Call 111 now
High temperature for 5 days or more, rash, or signs of dehydration	Call 111 for advice
Drinking, responding, comforted	Watch, fluids, rest — keep the course in Mona