A weight loss tool that starts with BMI + Intermittent Fasting.
Calculate - BMI, fasting window, and calorie deficit. Save and go!
Four Easy Steps
BMI calculator + fasting window
BMI Calculator
Intermittent Fasting Window
Calorie Deficit Calculator
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Foods to Avoid
Ultra-processed snacks
Items like chips, candy bars, and packaged pastries are often high in added sugars, refined grains, and unhealthy fats while offering little nutritional value.
Sugary beverages
Soda, sweetened iced tea, energy drinks, and many fruit juices can pack large amounts of added sugar, which is linked to weight gain and metabolic issues.
Refined carbohydrates
White bread, white pasta, and many breakfast cereals have been stripped of fiber and nutrients, causing quick spikes in blood sugar and low satiety.
Fried fast food
Deep-fried items such as fries, fried chicken, and onion rings tend to be calorie-dense, high in trans fats, and low in beneficial nutrients.
Processed meats
Bacon, sausage, hot dogs, and deli meats often contain high sodium levels and preservatives, and frequent consumption is associated with higher chronic disease risk.
High-sugar desserts
Cakes, cookies, donuts, and ice cream are rich in added sugars and saturated fats, which can contribute to weight gain when eaten frequently.
Dairy
Some dairy products, particularly full-fat varieties like whole milk, cheese, and butter, can be high in saturated fats and calories. Excessive intake may contribute to weight gain and elevated cholesterol levels in certain individuals. Additionally, many flavored yogurts and milk-based drinks contain added sugars.
Understand BMI, fasting, and calorie deficits
What BMI is (and what it isn’t)
Body Mass Index (BMI) is a quick screening metric that compares your weight to your height. It’s calculated as weight (kg) ÷ height (m²). In U.S. units, the formula uses a conversion factor so it still represents the same kg/m² measurement. BMI is widely used in public‑health reporting because it’s easy to measure at scale and correlates (imperfectly) with health risk across populations.
BMI is not a body‑fat test. It does not directly measure fat mass, muscle mass, bone density, or where fat is stored. That’s why athletic people with high muscle mass can show a “high” BMI even with low body fat, while others can have a “normal” BMI and still carry higher visceral (abdominal) fat. Age, sex, and ethnicity can also influence how BMI relates to health risk.
How to interpret BMI categories (adult screening ranges): Underweight (<18.5), Healthy (18.5–24.9), Overweight (25.0–29.9), and Obesity (≥30.0). These cutoffs are often used by clinical and public‑health organizations as a starting point for discussion, not a diagnosis. If your BMI is outside the healthy range, the next step is usually to consider other measurements (waist circumference, blood pressure, labs, lifestyle, and medical history) rather than treating BMI as the full story.
Alternatives and complements: Waist circumference/waist‑to‑height ratio can help estimate central adiposity (belly fat). Body‑fat testing (DEXA, BodPod, hydrostatic weighing) provides more direct insight. If you lift regularly and have noticeable muscle mass, consider a DEXA scan or similar body‑composition method.
Healthy weight range (how this tool calculates it)
This calculator uses the common “healthy BMI” range of 18.5–24.9 for adults. Once your height is known, we can compute the body‑weight range that would put you in that BMI band. That’s why the site can show a “healthy weight for your height” value even before you change anything else.
Important nuance: The healthy range is a guideline for adults in general, not a personalized medical target. For example, someone with a lot of muscle might feel and perform best slightly above 24.9, while another person might be healthiest nearer the middle of the range. If you’re using BMI for weight‑loss planning, it can be more realistic to aim for an initial milestone (for example, losing 5–10% of current body weight) and reassess how you feel, your labs, and your performance.
What “to reach healthy range” means here: The “to lose” number is the estimated amount of weight required to bring BMI down to 24.9 (the upper edge of the healthy range). That does not mean you must lose that exact amount. It’s simply a reference point you can use when setting goals.
Intermittent fasting: how to use it safely
Intermittent fasting (IF) is a meal‑timing approach that alternates fasting and eating windows. Common patterns include 12:12, 14:10, 16:8, and 18:6. The “best” window is the one you can follow consistently while maintaining adequate nutrition, sleep, and training quality.
Practical beginner approach: Start with 12:12 or 14:10 for 1–2 weeks. Focus on hydration (water, unsweetened tea/coffee) during the fasting window. Then, if you feel good (no dizziness, headaches, binge‑eating, or sleep disruption), you can experiment with 16:8. Many people find that pushing too hard too fast leads to rebound overeating, low energy, or poor workouts.
Who should be cautious: People with a history of eating disorders, those who are pregnant or breastfeeding, individuals under 18, and anyone on medications that affect blood sugar (especially insulin or sulfonylureas) should talk to a clinician before fasting. If you have diabetes, GERD, low blood pressure, kidney disease, or a demanding training schedule, you may need a different approach.
What IF does (mechanically): Fasting windows can make it easier to maintain a calorie deficit by reducing opportunities to snack. For many people, the benefit is behavioral. It does not “override” calorie balance; it’s simply a structure that can help you eat the right amount more consistently.
Calorie deficits: the part that drives weight loss
Weight loss requires a sustained energy deficit—burning more calories than you consume over time. Your body can compensate (appetite changes, activity changes), so the most sustainable plans are the ones that are modest, repeatable, and supported by habits: protein intake, resistance training, walking, and sleep.
What this slider represents: The calorie slider is a simple planning tool. It does not “know” your exact metabolism, but it helps you visualize how daily intake changes can affect expected weekly loss. Many clinical guidelines suggest targeting about 0.5–2.0 lb per week depending on your starting point, health status, and how aggressive you want to be—faster is not always better.
Make it work in real life: Aim for high‑satiety foods (lean proteins, vegetables, fruit, legumes, whole grains), and use a tracking method you’ll actually stick with (photo‑logging, portion templates, or app tracking). Combine a calorie deficit with strength training to preserve muscle, which helps long‑term maintenance.
Common questions
Start here: beginner-friendly guides
1) BMI for beginners: a practical explanation
Why BMI exists, how to use it, and how not to overreact to it.
Read the full article
BMI is popular because it’s simple: it turns height and weight into a single number that correlates with health outcomes across large groups of people. That makes it useful for researchers and for quick clinical screening. But “useful” doesn’t mean “perfect.” BMI is a starting point, not a diagnosis.
Here’s how to use BMI the right way: (1) treat the category as a risk flag, not a label; (2) pair it with other measurements such as waist circumference, blood pressure, activity level, and lab work; (3) focus on behaviors (nutrition, movement, sleep) rather than obsessing over the exact number.
Common misunderstandings: BMI can run high in muscular people, and it can underestimate risk in people with low muscle mass but higher visceral fat. That’s why we recommend DEXA or waist measurements if you lift or if your BMI seems “off” compared to how you look and perform.
If your BMI is in the overweight/obesity range, the most proven approach is not a “hack”—it’s building sustainable habits that create a modest calorie deficit while protecting muscle. The simplest wins are: increase daily steps, prioritize protein and fiber, strength train 2–4×/week, and manage sleep. Small consistency beats aggressive plans that crash after two weeks.
2) Intermittent fasting: picking a window you can keep
A realistic approach to 12:12, 14:10, and 16:8.
Read the full article
Intermittent fasting works best when it fits your life. People often jump straight to 18:6 or 20:4, then struggle with headaches, fatigue, or late‑night overeating. A smarter approach is to treat IF like progressive training: start easy, then build.
Week 1–2: 12:12 or 14:10. Keep your eating window consistent. Hydrate during the fasting window. If you drink coffee, keep it unsweetened. If you’re training, place your workout near the start or middle of your eating window so you can get protein afterward.
Week 3+: Move to 16:8 if you feel stable. The win here is structure: fewer eating occasions often means fewer calories without constant tracking.
Fasting should never feel like punishment. If you get dizzy, have sleep disruption, or find yourself binging, widen the eating window. Consistency is what produces results, not hero days followed by “reset Mondays.”
3) Calorie deficit basics: how to lose fat without feeling miserable
The four levers: intake, protein, steps, and strength training.
Read the full article
Calorie deficits sound simple—eat less than you burn—but the hard part is making the deficit sustainable. The best plans reduce hunger and preserve muscle.
Lever 1: Protein. Protein supports satiety and helps preserve lean mass. Build meals around a protein anchor (chicken, fish, eggs, Greek yogurt, tofu, lean beef, beans).
Lever 2: Fiber and volume. Vegetables, fruit, legumes, and whole grains add volume without massive calories. This is why “whole foods” diets are easier to maintain than ultra‑processed snack patterns.
Lever 3: Steps. Walking is low‑stress and repeatable. A simple goal is to gradually increase daily steps. Consistent walking can meaningfully change weekly energy balance.
Lever 4: Strength training. Losing weight without strength training often means losing muscle. Strength work tells your body to keep lean tissue while you diet.
Use the slider as a starting point, then adjust based on how you feel and how your progress looks over 2–3 weeks. If you’re stuck, measure portions for a few days (or use a photo‑logging app) to get clarity.
4) BMI doesn’t tell the whole story: what to track instead
Better signals: waist, photos, performance, and consistency.
Read the full article
If BMI is noisy for you, use signals that reflect body composition and health more directly. A few high‑signal metrics: waist circumference (or waist‑to‑height ratio), progress photos under consistent lighting, strength levels in key lifts, resting heart rate trends, and adherence to habits (steps, protein, sleep).
The goal is not a perfect number—it’s a body you can maintain with habits that don’t wreck your life. Track what reinforces that: consistency.
5) A simple 7‑day reset plan
A realistic week to regain control without extremes.
Read the full article
Day 1: Set a consistent sleep and wake time. Hydrate. Walk 20 minutes.
Day 2: Build two meals around protein + vegetables. Keep snacks simple.
Day 3: Do a short strength session (full body). Add steps.
Day 4: Choose a fasting window you can keep (12:12 or 14:10). Do not compensate by overeating later.
Day 5: Plan meals for the weekend. Remove one “trigger” food from immediate reach.
Day 6: Repeat strength or a longer walk. Prioritize protein at breakfast or first meal.
Day 7: Review: What was easiest? What was hardest? Keep the parts you can repeat next week.
This is not a “detox.” It’s a gentle reset toward consistency.
Why bmi2fast exists
bmi2fast is a lightweight web app that helps you:
- Calculate BMI and a healthy weight range
- Choose an intermittent fasting window that fits your day
- Estimate a calorie‑deficit plan and save a shareable PNG summary
- Explore U.S. obesity trend data from reputable public sources
We keep this tool simple on purpose: no accounts, no paywalls, and no hidden tracking beyond standard analytics. The intent is to help you make a plan you can follow—and to encourage sustainable habits rather than extremes.
If you’d like to contribute, suggest improvements, or report a bug, use the contact section below.
Questions, feedback, or partnerships
Fastest way: email us.
If you prefer, you can also include screenshots or a description of your device (iPhone/Android, browser) so we can reproduce issues.