Weight Loss Calculator for Wegovy: Reading the Numbers Honestly

What do weight loss calculators for Wegovy actually calculate?

Most tools you'll find online work the same way: you enter your current weight, sometimes your height or BMI, and the calculator applies a percentage from the published trial results to give you a projected end weight. The figure they're drawing on is almost always the STEP 1 trial result, roughly 15% average body-weight reduction over 68 weeks on semaglutide 2.4mg, as published in the New England Journal of Medicine. That's a solid, peer-reviewed number. The limitation is what gets stripped away in the calculation.

STEP 1 enrolled adults with obesity but without type 2 diabetes. All participants followed a reduced-calorie diet and increased their physical activity. The 15% is a mean: some people lost 7%, others lost over 20%. A calculator that returns a single tidy figure is averaging over that whole distribution and applying it to your starting weight as if your biology were identical to the median participant. It isn't, and neither is anyone else's.

There's also a gap in the data these tools use. The MHRA approved a 7.2mg single-dose Wegovy pen in April 2026, and trials at that dose reported average weight loss of around 20.7%, considerably higher than the 2.4mg figure. If a calculator was built before that approval, its projections for patients who ultimately reach the maximum dose will be meaningfully low. You can read about the full Wegovy treatment overview for context on how the dosing schedule works.

Why does the starting dose matter so much for what a calculator shows?

Wegovy treatment begins at 0.25mg weekly, stepping up roughly every four weeks toward the 2.4mg maintenance dose, and now potentially to 7.2mg. A calculator that plugs in the end-point figure tells you nothing about the journey: the weeks at lower doses when appetite suppression is milder, the plateau some people hit before their prescriber adjusts the dose, or the people who reach 7.2mg and find results closer to tirzepatide territory.

This matters practically. If you start treatment expecting a straight-line loss toward a calculated target, the reality of dose titration can feel slower than the number suggested. A question our prescribers hear regularly is why progress in the first 8–12 weeks looks modest compared to the projected total. The answer is that the calculation assumed you were already at maintenance dose, week one.

For a direct comparison of how Wegovy's dose escalation compares to another GLP-1 option, the Mounjaro versus Wegovy page covers the trial evidence side by side, including the SURMOUNT-5 head-to-head data. And if you're trying to understand how Ozempic and semaglutide compare for weight loss, that page clarifies what the two actually have in common and where they differ. The Wegovy versus Ozempic comparison explains exactly why those two medicines aren't interchangeable for weight loss.

What a calculator can't tell you about whether Wegovy is right for you

Eligibility for Wegovy is defined in the medicine's UK licence: adults with a BMI of 30 or above, or 27 or above if at least one weight-related condition is present (such as high blood pressure, high cholesterol or obstructive sleep apnoea). Lower BMI thresholds apply for some ethnic backgrounds under UK guidance. A calculator that returns a projected weight loss based on your starting weight is not an eligibility check.

It also can't flag contraindications. Wegovy is not recommended during pregnancy, breastfeeding or when trying to conceive. People with a history of certain thyroid or pancreatic conditions need a careful prescriber conversation before starting. Other medicines you take (including oral contraceptives) may be relevant to your suitability, since GLP-1 medicines can affect how quickly tablets move through your system. The NHS semaglutide page covers the key safety considerations that a projection tool will never ask about.

Separately, calculators say nothing about cost. Private Wegovy treatment is priced per pen, varies by dose, and the overall picture is worth understanding before you start, the Wegovy price breakdown on this site explains what legitimate UK providers include and what headline prices sometimes leave out. Worth checking before committing.

How should you use a weight loss projection, then?

As orientation, not instruction. If a calculator tells you that losing 15% of your starting weight would bring you below the threshold for a weight-related health condition, that's useful information to take into a clinical conversation. If it tells you that 20% loss would take you to a BMI you haven't seen in a decade, that's motivating context. What it shouldn't be is the reason you order a prescription medicine.

The more useful exercise is speaking to a prescriber who can look at your full picture: your starting weight, your medical history, what other treatments you've tried, and which medicine fits your circumstances. If Wegovy isn't the right fit, alternatives like liraglutide versus Wegovy or tirzepatide may be more appropriate, that's a clinical call, not a calculator output.

At nume, every consultation is reviewed by a GPhC-registered Independent Prescriber (a real clinician, the same day) so a conversation about realistic expectations is built into the process, not an optional add-on. You can explore what that process involves or take a look at our clinical team if you want to understand who's reviewing your information. The weight loss treatment overview is also a good starting point if you're still deciding which option to explore. When you're ready, check your eligibility through a free consultation, it's the step that turns a projected number into an actual plan.