Using a semaglutide calculator online — what it tells you and what only a prescriber can

Step 1: what a BMI and eligibility calculator actually does

Most semaglutide calculators you find online start with the same two inputs: your height and your weight. From those they calculate your body mass index and then check it against the UK licensing criteria for Wegovy. The licensed threshold is BMI 30 or above; people with a BMI between 27 and 29.9 qualify if they have at least one weight-related health condition such as high blood pressure, raised cholesterol, obstructive sleep apnoea or type 2 diabetes. Some tools also ask about ethnic background, because UK guidance applies thresholds that are 2.5 kg/m² lower for South Asian, Chinese, Middle Eastern, Black African and African-Caribbean backgrounds. The semaglutide overview page sets out the full eligibility picture if you want to check before doing anything else.

The NHS BMI calculator at NHS.UK is a reliable free tool for the BMI part of that calculation. What an online semaglutide calculator adds is the comparison against the medicine's licensed thresholds, useful context, but not a clinical decision. A prescriber still needs to look at your medical history, your current medicines, and any conditions that might make semaglutide unsuitable, before a prescription is issued.

Step 2: understanding dose-schedule and titration calculators

A second category of tool maps out the standard titration pathway. Wegovy's dose schedule starts at 0.25 mg weekly for four weeks, then moves through 0.5 mg, 1.0 mg and 1.7 mg before reaching the 2.4 mg maintenance dose, with approximately four weeks at each level. Some calculators will display this as a timeline based on a start date you enter, so you can see roughly when you would expect to reach each stage. The Wegovy calculator on this site works on that principle.

These tools are genuinely useful for setting expectations. The STEP 1 trial, published in the New England Journal of Medicine, found that semaglutide at 2.4 mg produced an average body-weight reduction of around 15% over 68 weeks in adults with obesity, but that figure reflects the full titration, not the early weeks at 0.25 mg or 0.5 mg. Knowing the schedule helps you understand why results build gradually. What a timeline calculator cannot do is tell you whether to hold a dose longer because of side effects, or whether your prescriber thinks you should go more slowly. That judgement belongs to the clinician, not the tool.

Step 3: compounding calculators, and why they don't apply to licensed Wegovy

If you search for a peptide calculator for semaglutide, or look into BAC water calculators and dilution calculators, you will find tools built for a very different context. These are associated with compounded semaglutide, a powder that must be reconstituted before injection, typically sourced outside the licensed supply chain. Compounded semaglutide is not licensed for human use in the UK. The MHRA has warned about counterfeit and unlicensed weight-loss products sold online, and mixing calculations are a marker of that market, not a feature of legitimate treatment. Licensed Wegovy pens come pre-filled at fixed doses, from the manufacturer Novo Nordisk. There is nothing to mix or dilute. You can read more about what semaglutide mixing calculators actually describe, and why they sit outside the UK licensed context, on that page.

It is worth knowing this distinction because the terms overlap online in confusing ways. If a seller is directing you toward mixing guides for a weight-loss medicine, that is a red flag, not a feature. For guidance on finding semaglutide through a legitimate route, the Wegovy where to buy page explains what to look for and how to verify any online pharmacy on the GPhC register.

Step 4: from calculator result to clinical assessment

If a calculator suggests you likely meet the eligibility criteria, the next step is a clinical consultation. At nume, that means completing a free health questionnaire which is then personally reviewed by a GPhC-registered Independent Prescriber, a real clinician reads your answers, the same day. The consultation covers your BMI, your relevant medical history, your current medicines (some interact with semaglutide), and whether Wegovy or an alternative is the better clinical fit for you. Semaglutide is not suitable during pregnancy, breastfeeding or when trying to conceive, and is not licensed for under-18s. A calculator can flag none of that.

If you are weighing up the financial side alongside eligibility, the weight-loss treatments page sets out the context for private treatment costs and what is included in a transparent price. The calculator is a reasonable place to start. The consultation is where an actual decision gets made. If you are ready for the clinical step, you can start your free consultation with our prescribers today.