Calorie Calculator: How to Estimate Your Daily Needs on a GLP-1 Journey

A calorie calculator works in two steps: first it estimates your resting energy needs, then it scales that up for movement. From there, you choose a goal — maintain, cut, or build — and the calculator adjusts the number. The output is an estimate, not a prescription, but it's a reliable starting point that you can refine over a few weeks of tracking.

Step 1: estimating your BMR

Your basal metabolic rate (BMR) is the energy your body uses just to keep you alive — breathing, circulation, organ function, basic cell repair. It's typically the biggest chunk of your daily burn. Most calculators use the Mifflin-St Jeor equation, which factors in your weight, height, age and sex. If you want to look at just this piece on its own, our BMR estimation guide walks through it in more detail.

Step 2: adding activity to get TDEE

BMR is then multiplied by an activity factor to give your total daily energy expenditure (TDEE) — roughly what you burn in a typical day. Sedentary, lightly active, moderately active and very active all carry different multipliers. Be honest here; most people overestimate how active they are, which inflates the calorie number.

Step 3: adjusting for your goal

Once you have TDEE, you adjust:

• Maintenance: eat around your TDEE. See our maintenance calorie calculator guide for more on this.
• Cut / weight loss: a moderate deficit — often 15–25% below TDEE — is a common starting point. Our calorie deficit explainer covers this, and the weight loss calculator overview shows how the numbers translate into expected progress over time. You can also browse the cut calorie approach if that's the framing you prefer (mentioned in plain text as a sibling concept).
• Build / bodybuilding: a small surplus, generally with higher protein. See the bodybuilding calorie calculator guide.

Why this matters on Mounjaro or Wegovy

GLP-1 medicines reduce appetite by acting on pathways involved in hunger and fullness (and, for tirzepatide, also GIP). Many people on these medicines find they naturally eat less — which is part of the point — but it can swing too far. Going too low on calories can leave you fatigued, hair-shedding, irritable, and short on the protein needed to protect lean mass while losing fat. A calorie calculator gives you a numerical floor and a target to keep food intake sensible, not just minimal.

Different calculator names, same idea

You'll see calorie calculators under lots of names — "calorie intake calculator", "daily calorie calculator", a "cut calorie calculator", or branded versions like a Mayo Clinic-style calorie calculator. They all use broadly the same maths (BMR + activity ± goal adjustment). The differences are mostly in the activity multipliers and how aggressive the default deficit is. Helpful related reads:

• Calorie intake calculator overview
• How many calories should I eat a day
• How many calories can I have in a day
• How many calories a day can I eat
• How many calories a day should I consume
• How many calories must I eat a day
• Understanding calories
• A second look at calorie calculators
• Macros-to-calorie conversion

Typical educational ranges

As general educational ranges (not personalised targets), many adults' maintenance needs sit somewhere between roughly 1,600 and 2,800 calories a day, depending on size, age, sex and activity. A modest deficit for steady fat loss often lands a few hundred calories below that. For specific numbers that suit you — especially if you have medical conditions, are on multiple medicines, or have a history of disordered eating — talk to your prescriber or doctor or a registered dietitian. The NHS guidance on eating well is a sensible general reference for balanced intake.

Why your calorie number isn't fixed forever

As you lose weight, your TDEE drops — a smaller body needs less energy. That's why progress can slow and what worked at week 4 may not work at week 16. Recalculating every few kilograms lost is a good habit, and tracking real intake against real outcomes is more useful than trusting a single number forever.

The hardest part of using a calorie calculator isn't the maths — it's actually logging food consistently enough to know whether you're hitting the number. That's where GLP Trackr is designed to take the friction out, especially when GLP-1 appetite changes make food feel less interesting to think about.

Effortless food logging built for GLP-1 life

Point your phone at your plate and the AI photo scan estimates calories, protein and macros in seconds — no manual searching, no weighing every ingredient. When you do want precision, the barcode scanner handles packaged foods, and the search database covers the rest. On days when appetite is low and you're only managing a few bites, two seconds of logging is genuinely doable.

Set your target once, see it every day

You can plug in a calorie target — from a calculator, your dietitian, or based on what's working for your body — and GLP Trackr tracks against it daily. Protein, water, fibre and step targets sit alongside, so you're not just chasing a calorie number in isolation. That matters on a GLP-1 journey, where protecting lean mass and staying hydrated are often more important than squeezing the deficit lower.

Insights that connect food to progress

Logging without insight is just a chore. The insights view connects your calorie intake to your weight trend, energy, mood and side effects over time, so you can see what's actually working — not guess. If progress stalls, the plateau view helps you spot whether intake has crept up, activity has dropped, or whether your body is simply asking for a recalculated target.

A note on calorie numbers and your health

A calorie target is general nutrition guidance, not a medical prescription. If you've been given specific intake advice by your prescriber or doctor — for example because of diabetes, thyroid conditions, pregnancy, or another consideration — follow their guidance rather than a generic calculator. GLP Trackr is here to help you record and review, not to replace the conversation with the professional who knows your history. If you notice persistent fatigue, hair loss, dizziness, or other worrying symptoms while losing weight, contact your healthcare professional.

Get started

If you're already on Mounjaro or Wegovy, getting your calorie target dialled in is one of the highest-leverage things you can do. Snap your meals, hit your protein, watch the trend — and let the app do the spreadsheet work in the background. GLP Trackr is free to try for 7 days on the App Store and Google Play — set your calorie target, scan your first meal, and see your week come together in one place.