The short answer
Most of the time it's one of two things: you're eating more than you think, often on weekends, or you're losing fat while gaining muscle and the scale can't tell. Drinks, sleep, and a body that got smaller round out the list.
Your metabolism didn't break at 40. A large 2021 study of metabolism across the lifespan found it holds steady from about age 20 to 60.
The 6 reasons
1. You're eating more than you think
A classic study found people who said they couldn't lose weight were underreporting their food by nearly half. Bites, tastes, and handfuls count. Finishing the kids' chicken nuggets counts.
2. Weekends are erasing your week
Eat 500 calories under your needs Monday through Thursday and you've banked 2,000. Eat 700 over on Friday, Saturday, and Sunday and you've spent 2,100. It's saving all week and blowing the paycheck Saturday night.
3. You're drinking calories
Four beers is about 600 calories. A big sweetened coffee drink runs 300 to 400. None of it fills you up.
4. You're losing fat and gaining muscle
If your waist is shrinking, the scale isn't telling the whole story. More here: losing inches but not weight.
5. You're short on sleep
Short sleep raises your hunger hormones and makes the pantry louder. It also shifts what you lose toward muscle instead of fat.
6. Your body got smaller, so it needs less
A lighter body burns fewer calories. The plan that took off your first 15 pounds is now close to a maintenance plan. It's a car that gets better mileage after you unload the trunk.
The 3 moves
Move 1: Track everything for 7 days, weekend included. Not forever. One honest week shows you the leak.
Move 2: Set one weekend rule. Pick one: two drinks max, protein first at every meal, or no eating after the kids go to bed. One rule, not five.
Move 3: Judge by 3 weeks, not 3 days. Use your weekly weight average plus your Sunday waist measurement. If both are flat for 3 to 4 weeks, trim 200 to 300 calories a day and hold.
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I'm Jason, a dad of two in my 40s. Every Tuesday and Thursday I send one idea and three moves for dads who want to drop body fat and build muscle at the same time. Five minutes to read. Free.
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Common questions
Is it my thyroid or testosterone?
Sometimes, but it's much less common than the six reasons above. If you've tracked honestly for 8 weeks and neither your weight nor your waist has moved, see your doctor and ask for bloodwork. Some medications affect weight too, so bring your list.
How long before the scale should move?
Give any new plan 2 to 3 weeks before you judge it. The early weeks are noisy with water.
Do I need more cardio?
Not first. Cardio burns calories, but they're easy to eat right back. Fix the food leak, keep lifting, and walk more.
Keep reading
I'm not a doctor. If you have a medical condition or take medication that affects your weight, check with yours before changing how you eat or train.