How Many Calories and How Much Protein Do I Actually Need? (Free Calculator)

Quick version: most people guess. They pick a round number — 1,500 calories, 100 grams of protein — because it sounds about right. Then they wonder why the scale won''t budge, or why they''re hungry by 3 p.m., or why they feel weak in the gym.

Good news: there''s a real formula for this. It''s called Mifflin–St Jeor, it''s been the gold standard since 1990, and we just built it straight into the free SmashMeals Quick Plan Builder.

Why your bodyweight × 12 isn''t the answer

The internet loves shortcuts. "Multiply your bodyweight by 12 if you''re sedentary, 15 if you''re active." It''s easy to remember and it''s wrong for most people.

Two people who weigh 180 lb can have wildly different calorie needs. A 25-year-old 6''2" man burns hundreds more calories at rest than a 55-year-old 5''4" woman at the same weight. Bodyweight alone misses sex, age, and height — three of the biggest variables in metabolism.

Enter Mifflin–St Jeor

Published in the American Journal of Clinical Nutrition in 1990 and validated in dozens of follow-up studies, the Mifflin–St Jeor equation is the formula most registered dietitians and doctors actually use. It predicts your basal metabolic rate (BMR) — the calories your body burns just keeping you alive — within about 10% for most adults.

Here''s the formula (you don''t have to do this; the calculator does it for you):

• Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
• Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161

Then you multiply BMR by an activity factor (1.2 sedentary up to 1.725 very active) to get your total daily energy expenditure (TDEE) — the number of calories you actually burn in a day.

How much protein do I need?

This one trips up almost everyone. The official RDA (0.36 g/lb) is the bare minimum to avoid deficiency — not the amount that helps you lose fat, build muscle, or feel full.

For people actively trying to change their body, most evidence-based guidelines (Academy of Nutrition and Dietetics, ISSN, ACSM) land in this range:

• Losing weight: ~1.0 g per pound of goal bodyweight (preserves muscle in a deficit)
• Building muscle: ~0.9 g per pound of goal bodyweight
• Maintaining: ~0.8 g per pound of current bodyweight
• Post-bariatric or GLP-1 user: 60–80 g/day minimum, per ASMBS guidance

The "I''m on a GLP-1" question

If you''re on Ozempic, Wegovy, Mounjaro, or Zepbound, your appetite is dialed way down — which is the point. The risk is that you eat so little that you lose muscle along with fat, get foggy, or hit a wall.

Our calculator has a GLP-1 / post-bariatric checkbox. When you tick it, the deficit cap drops from 750 cal/day to 500 cal/day, and the protein floor stays locked at 60 g — so every bite earns its keep.

Built-in safety rails

We didn''t build an aggressive calculator. We built a sustainable one. The CDC and Mayo Clinic both recommend losing 1–2 lb per week for long-term success. Our caps:

• Never below 1,200 cal/day for women, 1,500 cal/day for men
• Max 750 cal/day deficit (500 for GLP-1/bariatric)
• Max ~2 lb/week pace
• If you ask for something more aggressive, the calculator pulls you back and explains why

OK, I have my numbers. Now what?

This is where most calculators leave you stranded — congrats on knowing you need 1,650 cal and 130 g protein. Now go cook 21 meals this week. Good luck.

The SmashMeals planner doesn''t do that. The second the calculator finishes, it pulls real meals from this week''s 100% gluten-free menu that hit your numbers — choose 1, 3, 5, or 7 days, pick a diet style (keto, low-carb, high-protein, bariatric, GLP-1, low-cal), and you''ve got a printable, emailable, orderable plan.

Where the meals come from

Every meal is made fresh in our dedicated 100% gluten-free kitchen in Kingsport, Tennessee. Not a "gluten-free station." The whole building. That means no shared gluten-containing equipment — suitable for people with celiac disease.

Choose an available pickup location or enter your address to check Tri-Cities home delivery and its charge. We also offer $30 flat-rate FedEx Ground shipping for eligible addresses. Arrival timing depends on the destination and carrier conditions. Local meals are prepared fresh. Shipped orders are frozen before leaving the kitchen.

One important disclaimer

The calculator gives you general guidance based on validated science — but it''s not medical advice. Individual needs vary with health conditions, medications, pregnancy, and a hundred other factors. Talk with your doctor or a registered dietitian before starting a weight-loss, high-protein, or post-bariatric plan. We''ll be here when you''re ready.

Local areas we serve

Review pickup locations, local delivery eligibility and shipping information for the actual destination you will use.

Related reading

• News: SmashMeals Launches Personalized Calorie & Protein Calculator
• Stop Guessing What to Order: The New Ordering Helper
• GLP-1 Friendly Meals · Bariatric Meals · High-Protein Meals