Why Every Calculator Gives You a Different Number
I tested six different TDEE calculators with identical stats (32M, 185 lbs, 5'10"). Want to guess what happened?
- - Calculator A: 2,340 calories
- - Calculator B: 2,610 calories
- - Calculator C: 2,180 calories
- - Calculator D: 2,450 calories
That's a 430-calorie spread. What gives?
Different formulas. Some use Mifflin-St Jeor (more accurate, developed 1990). Some use Harris-Benedict (older, from 1918, revised 1984). Some use Katch-McArdle (needs body fat %, most accurate if you have that data).
The Mifflin-St Jeor equation is generally considered the gold standard now. It's been validated in multiple studies and tends to be more accurate for modern populations. Harris-Benedict was developed over a century ago when people were generally more active—no desk jobs, no cars, no Netflix. So it tends to overestimate for most of us.
Katch-McArdle is technically the most accurate, but only if you have a reliable body fat percentage. And no, your home scale that says you're 18% body fat isn't reliable. You need a DEXA scan or Bod Pod. Those bathroom scales with the metal footpads? They can be off by 5-8%. That error gets amplified in the final calorie calculation.
Here's my advice: pick ONE calculator, use it for 3 weeks, track your actual weight trend. If you're losing when you shouldn't be, add 200 calories. If you're gaining when trying to maintain, subtract 200. The formula is your starting point, not the finish line.
Your real TDEE is whatever the scale tells you it is after tracking honestly for a few weeks. Numbers don't lie. If you're "eating 1,800 calories" and not losing weight, you're not eating 1,800 calories. Either the calculator was wrong, or your tracking is off, or both.
The Activity Level Thing That Everyone Gets Wrong
This is where people screw up. I'm talking from experience here.
Sedentary (1.2x multiplier):
Desk job. You drive to work, sit 8 hours, drive home, sit on the couch. Even if you hit the gym 3-4x per week for an hour, you're still sedentary. That's 23 hours of not training. You're sedentary.
I lift 4 days a week, walk my dog for 20 minutes daily. I'm sedentary. Took me forever to accept this. My ego wanted to click "moderately active" because I work out regularly. But the math doesn't lie. Four hours of lifting per week divided by 168 hours total? That's 2.4% of my week being active. The rest is sitting at my desk, driving, watching Netflix.
Lightly Active (1.375x):
You're on your feet a decent amount. Teacher walking around the classroom all day. Retail worker stocking shelves. Stay-at-home parent chasing toddlers around. You're moving throughout the day, not just during dedicated workout time. My sister's a teacher and she hits 12,000 steps just from work, before any intentional exercise. That's lightly active.
Moderately Active (1.55x):
Physical job AND you train. You're a server on your feet for 8-hour shifts AND you go to the gym after. Construction worker who also does cardio on weekends. It's both, not either/or. Just having a physical job isn't enough if you sit the rest of the time. Just working out isn't enough if your job is sedentary.
Very Active (1.725x):
You train 6-7 days per week with intense sessions, or you have an extremely physical job like landscaping or working for a moving company. Most people never qualify for this. I tried it once during a bulk. Burnt out in three weeks. Couldn't sustain it.
Extremely Active (1.9x):
Competitive athlete training 10+ hours per week. Manual laborer who also trains hard daily. Very few people are actually here. If you're Googling calorie calculators on a Tuesday afternoon, you're probably not in this category. No offense.
The biggest mistake: thinking your gym time alone makes you "active." It doesn't. Three hours per week at the gym is 3 hours. There are 168 hours in a week. Do the math.
When in doubt, go one level lower than you think. You can always add calories back if you're losing too fast. Way easier than trying to figure out why you're not losing when you're "eating at a deficit." Trust me on this one.
Formulas Explained (Without the Academic Nonsense)
Mifflin-St Jeor (use this one):
More accurate for modern populations. Accounts for the fact that we're generally less active than people in 1918. It was developed by analyzing actual metabolic data from thousands of people in the 1990s, not theoretical estimates from a century ago.
The formula looks like this:
Men: (10 × weight in kg) + (6.25 × height in cm) - (5 × age) + 5
Women: (10 × weight in kg) + (6.25 × height in cm) - (5 × age) - 161
Harris-Benedict (older formula):
Tends to overestimate by 5-10% for sedentary people. Still used by some calculators because it's been around longer and people recognize the name. But newer research shows it's not as accurate for people who sit most of the day. Which is most of us.
Katch-McArdle:
Uses body fat percentage instead of sex. Most accurate IF you know your actual body fat % (not what your bathroom scale says). If you don't have an accurate body fat measurement from DEXA or Bod Pod, don't use this. You'll just be feeding bad data into a good formula.
Then you multiply your BMR by your activity multiplier to get TDEE. BMR is what you'd burn in a coma. TDEE is what you actually burn with daily activity.
Example: My BMR is 1,847 calories. I'm sedentary (1.2x). My TDEE is 2,216 calories. That's my maintenance. To lose one pound per week, I need a 500 calorie deficit, so I eat 1,716 calories. Simple math. The hard part is actually sticking to it.
Cutting, Bulking, and Maintenance Targets
Maintenance: Eat at your TDEE. Your weight stays stable (within 2-3 lbs of water weight fluctuation). This is your baseline. Everything else is calculated from here.
Cutting (fat loss):
- - Conservative: -300 to -500 calories (lose 0.5-1 lb per week)
- - Aggressive: -750 to -1000 calories (lose 1.5-2 lbs per week)
Don't go below 1,500 calories if you're male or 1,200 if you're female without medical supervision. Your body needs minimum fuel for hormones and organ function. Going too low tanks your testosterone, messes with your thyroid, and makes you feel like garbage. Not worth it.
Lean Bulking (muscle gain, minimal fat):
- - Beginner: +300 to +400 calories (gain 0.5-1 lb per week)
- - Intermediate: +200 to +300 calories (gain 0.5 lb per week)
- - Advanced: +100 to +200 calories (gain 0.25-0.5 lb per week)
Aggressive Bulk:
+500+ calories. You'll gain muscle faster but also significant fat. Only worth it if you're very underweight or don't care about staying lean. Some people like the "bulk and cut" cycle. I don't. Too much time spent fat.
I prefer lean bulking. Yeah, it's slower, but I don't have to do a brutal 3-month cut afterward. I can stay within 10 pounds of where I want to be year-round. Way more sustainable.
The Two-Week Reality Check
Here's your actual protocol. This is what actually works.
Week 1: Calculate your TDEE using one of the formulas above. Eat at that number every day. Weigh yourself daily, first thing in the morning after bathroom, before eating. Track it in a spreadsheet or app. Don't skip days.
Week 2: Keep eating the same calories. Keep weighing daily. No changes yet. You're collecting data. This is the boring part but it's important.
End of Week 2: Average your weights from each week. Compare them. Did you:
- - Lose weight? Your calculated TDEE is too high. Add 100-200 calories.
- - Gain weight? Your calculated TDEE is too low. Subtract 100-200 calories.
- - Stay the same (within 1 lb)? That's your actual TDEE. Congrats, you found it.
Now you have YOUR real number, not what some formula guessed. This is gold. Write it down.
From there:
- - Want to cut? Subtract 500 from your real TDEE
- - Want to bulk? Add 300-400 to your real TDEE
- - Want to maintain? Keep eating your TDEE
Reassess every 10-15 pounds of weight change. Your TDEE drops as you get lighter (smaller body burns fewer calories) and rises as you get heavier. A 200-pound person burns way more than a 160-pound person just existing.
I track my weight in a spreadsheet with a 7-day moving average. Smooths out the water weight noise from salty meals, hard workouts, and weekend drinking. Highly recommend. Makes it way easier to see the actual trend instead of freaking out over daily fluctuations.
Exercise Calories: To Eat Them Back or Not?
Fitness trackers lie. Your Apple Watch says you burned 600 calories in your workout? You probably burned 350-400. Maybe. They're notorious for overestimating, especially for weight training.
If you're using the TDEE method (which includes activity level), DO NOT eat back exercise calories. That's double-counting. Your activity multiplier already accounts for your workouts. Adding extra calories on top is how you end up not losing weight despite "being in a deficit."
If you're using the NEAT method (sedentary TDEE + adding exercise), then yes, eat back 50-75% of what your tracker says. Not 100%, because they overestimate. If your watch says 400 calories, eat back 200-300.
I use TDEE method because it's simpler. Same calories every day, no mental math. I don't have to think about whether today's workout "earned" me an extra snack. The consistency makes it easier to track trends.
Exception: if you do something truly insane (ran a marathon, 5-hour hike with a heavy pack, full day of moving furniture), add 300-500 calories that day. But your regular gym sessions? Your three-mile run? Your hour of lifting? Already accounted for in your activity level. Don't double dip.
Reality Check: Tracking Honesty
You know that handful of almonds? 200 calories.
That "splash" of cream in your coffee? 100 calories across three cups.
That bite of your kid's mac and cheese? 80 calories.
Weekend eating where you "eyeball it"? You're off by 500+ calories. Easy.
Most people underestimate their intake by 20-30%. I did. Everyone does. It's not a moral failing, it's just human nature. We're terrible at estimating portions.
Get a food scale. Use it for two weeks. You'll be shocked how wrong your portion estimates are. What you think is 2 tablespoons of peanut butter is actually 4 (360 calories vs 180). That "medium" banana is actually large (150 calories vs 105). Your cooking oil? You're using way more than you think.
You don't have to track forever. But track accurately for at least a month so you learn what portions actually look like. Then you can eyeball it with some accuracy. But that first month? Weigh everything. Yeah, it's annoying. Do it anyway.
Good Resources That Aren't Trying to Sell You Stuff
- - examine.com (nutrition research database, no BS)
- - Renaissance Periodization YouTube channel (Dr. Mike Israetel, evidence-based)
- - Stronger By Science (Greg Nuckols, actual research breakdowns)
- - USDA dietary guidelines (boring but accurate baseline info)
- - Precision Nutrition calculator (free, well-designed, no signup wall)
Avoid: Anyone selling a "metabolism boosting" supplement. Anyone claiming you can lose 10 lbs in a week without losing muscle. Anyone with a "one weird trick" in their headline.
This isn't medical advice. If you have metabolic conditions (thyroid issues, PCOS, diabetes), hormonal problems, or eating disorder history, work with a registered dietitian who understands your specific situation. Internet calculators are a starting point, not a replacement for professional guidance.