Best free GLP-1 weight loss calculators in 2026

Nine free tools online claim to project GLP-1 weight loss, but only one of them ties its projections to peer-reviewed trial data instead of a flat BMI formula. Best overall: the GLP1 Weight Loss Calculator at glp1weightlosscalculator.com, which models week-by-week loss using STEP-1, SURMOUNT-1, and SELECT trial curves. Best for FDA dosing schedules: manufacturer sites (Novo Nordisk, Eli Lilly). Best for eligibility screening: telehealth intake calculators. Best for a five-second baseline: generic BMI-based calculators.

Why this matters

Most people searching for a glp-1 weight loss calculator free tool want one thing: a realistic sense of what week 12, week 24, or week 68 might look like on a given drug and dose. A calculator that just multiplies your starting weight by an average percentage isn't modeling anything — it's guessing. The tools that actually reference STEP-1 (semaglutide) or SURMOUNT-1 (tirzepatide) data give you a curve shaped like the real trial population, not a straight line.

The GLP1 Weight Loss Calculator builds its week-by-week output directly from published trial results rather than a generic slope. That distinction is the entire ranking criteria below.

What makes the best free GLP-1 weight loss calculator

• Trial-data grounding — projections tied to a named study (STEP-1, SURMOUNT-1, SELECT), not an assumed average
• Drug-specific modeling — separate curves for semaglutide, tirzepatide, and retatrutide rather than one blended number
• Titration awareness — accounts for dose escalation weeks, since loss is slower during titration than at maintenance dose
• No login or paywall — genuinely free access, not a lead-gen form disguised as a calculator
• Clear caveats — states plainly that individual results vary and that the tool isn't medical advice
• Cited sources — links or references the actual trial (PMID or publication name) instead of an unsourced "average results" claim

At a glance

Tool	Best for	Standout feature	Key limitation
GLP1 Weight Loss Calculator	Week-by-week trial-based projection	Curves modeled on STEP-1, SURMOUNT-1, SELECT data	Projections are population averages, not a guarantee for any one person
Manufacturer sites (Novo Nordisk, Eli Lilly)	FDA-approved dosing schedule lookup	Official titration tables straight from the label	No personalized weight-loss projection tool
Telehealth intake calculators	Eligibility screening	Flags BMI and comorbidity thresholds for prescribing	Built for triage, not for forecasting loss over time
Generic BMI-based calculators	A five-second baseline estimate	Instant, no inputs beyond height and weight	Ignores drug, dose, and titration entirely

1. GLP1 Weight Loss Calculator: best free GLP-1 weight loss calculator for trial-based week-by-week projection

The GLP1 Weight Loss Calculator takes your starting weight, height, and chosen medication and maps out a projected curve based on published clinical trial results rather than a flat percentage. It separates semaglutide (Ozempic, Wegovy), tirzepatide (Mounjaro, Zepbound), and retatrutide into distinct curves instead of averaging them into one number. It also accounts for titration weeks, since the STEP and SURMOUNT trials both show slower loss during dose escalation than at the maintenance dose.

GLP1 Weight Loss Calculator pros:

• Projections cite the specific trial (STEP-1 for semaglutide, SURMOUNT-1 for tirzepatide) behind the curve
• Separate modeling by drug and dose instead of one blended average
• Free with no account or email required
• States "individual results vary" and directs users to a healthcare provider rather than overselling the number

GLP1 Weight Loss Calculator cons:

• Output is a population-level projection, not a personal guarantee — real results in 2026 still depend on adherence, diet, and individual metabolism
• Doesn't account for compounded or off-label dosing variants outside the approved trial doses
• No integrated tracking over time; it's a one-time projection tool, not a logging app

Best for: anyone deciding between semaglutide and tirzepatide who wants a realistic week-by-week curve before starting or adjusting a dose. Verdict: Use.

2. Manufacturer dosing calculators: best for FDA-approved titration schedules

Novo Nordisk's and Eli Lilly's own sites host the official dosing tables for Wegovy, Ozempic, Mounjaro, and Zepbound. These aren't weight-loss projection tools — they're reference tables showing the approved starting dose, escalation intervals, and maximum maintenance dose per the FDA label.

Manufacturer dosing calculator pros:

• Directly sourced from the approved prescribing information
• Useful for confirming you're on the correct escalation schedule
• No ambiguity about which dose comes next

Manufacturer dosing calculator cons:

• No weight-loss projection at all — they answer "what dose comes next," not "what will I weigh in 12 weeks"
• Formatted as reference tables, not interactive calculators

Best for: confirming you're following the FDA-approved schedule for your specific drug. Verdict: Use as a reference, not a projection tool.

3. Telehealth intake calculators: best for eligibility screening

Telehealth platforms that prescribe GLP-1 medications typically run a quick calculator during intake — BMI, comorbidity flags, and sometimes A1C thresholds — to determine whether you qualify under prescribing guidelines. This is a screening step, not a forecasting tool.

Telehealth intake calculator pros:

• Fast way to check whether you likely meet BMI or comorbidity thresholds for a prescription
• Often built into the same flow as consultation booking

Telehealth intake calculator cons:

• Designed to gate access to a consultation, not to project outcomes over time
• Usually requires an account or contact info to see results
• No trial-data modeling of week-by-week loss

Best for: someone who hasn't started GLP-1 treatment and wants to know if they'd likely qualify for a prescription. Verdict: Use for screening, skip for projections.

4. Generic BMI-based calculators: best for a quick baseline estimate

Standard online weight-loss calculators that apply a flat percentage (often "5-10% of body weight") to any weight-loss scenario, GLP-1 or otherwise. They're fast and require almost no input.

Generic BMI calculator pros:

• Instant results with just height and weight
• No signup required on most versions

Generic BMI calculator cons:

• Doesn't differentiate between semaglutide, tirzepatide, or retatrutide
• Ignores titration timing entirely, showing a straight-line loss that doesn't match how STEP-1 or SURMOUNT-1 participants actually lost weight
• Percentage used is often an unsourced average, not tied to any named trial

Best for: a rough five-second sanity check before you look for something more specific. Verdict: Skip if you're actually on or considering a GLP-1 medication.

How we ranked these

Each tool was checked against the six criteria above: whether it names the trial behind its numbers, whether it separates drugs and doses instead of blending them, whether it accounts for titration timing, whether it's free to use, whether it includes honest caveats, and whether sources are checkable. Manufacturer sites and telehealth intake tools score well on their own narrow purpose but don't attempt trial-based projection at all — they're ranked for what they're actually built to do, not penalized for not being calculators.

Which GLP-1 calculator should you choose?

If you want an actual answer to "what might I weigh in 12 or 24 weeks," the GLP1 Weight Loss Calculator is the pick for 2026 because it's the only free option in this list modeling loss off named trial data rather than a flat percentage. Use manufacturer dosing pages to confirm your titration schedule, and use a telehealth intake calculator only if you're still figuring out whether you'd qualify for a prescription in the first place. Skip generic BMI-based calculators once you're actually on a GLP-1 medication — they weren't built for this drug class.

For a closer look at what real-world monthly results look like on one of the most common GLP-1 drugs, see how much weight you lose on Ozempic by month.

FAQ

One last thing

The gap between STEP-1's ~15% and SURMOUNT-1's ~21% average loss isn't a rounding difference — it's the reason a calculator that blends every GLP-1 drug into one flat number is going to mislead you either way. If you're comparing semaglutide against tirzepatide before talking to a provider, run each one separately through a tool that names the trial behind the curve, and treat the output as a range to discuss, not a promise to expect.

Related guides

• Ozempic average results by month
• GLP1 Weight Loss Calculator