The short answer
If you want to lose weight, eat about 15–25% fewer calories than you burn in a typical day. For most adults that lands somewhere between 1,500 and 2,400 calories per day, but the right number for you depends on your size, activity, and goal pace. Use the free calculator below to get a starting point, then adjust based on real results over 2–3 weeks.
Why "deficit" is the only number that matters
Weight loss is a function of energy in vs. energy out averaged over time. You can argue about which foods make a deficit easier to maintain (high-protein, high-fiber wins, every time), but a deficit is what actually moves the scale. Anyone selling you a magic ratio without addressing total calories is selling you something else.
Two numbers do the work:
- TDEE — your Total Daily Energy Expenditure. The calories you burn per day, all-in.
- Deficit size — how far below TDEE you eat.
Subtract the second from the first and you have your target.
Step 1: Estimate your TDEE
TDEE has four components:
- BMR (Basal Metabolic Rate) — calories your body burns at rest. Roughly 60–70% of TDEE for most people.
- TEF (Thermic Effect of Food) — calories burned digesting food. Roughly 10%.
- NEAT (Non-Exercise Activity Thermogenesis) — fidgeting, walking, standing. Highly variable: this is where two people with identical workouts can differ by 500+ calories per day.
- EAT (Exercise Activity Thermogenesis) — your formal training.
A formula won't perfectly capture NEAT, but a good starting estimate is:
TDEE ≈ BMR × Activity Multiplier
Use the calculator below — it implements the Mifflin-St Jeor equation, which the Academy of Nutrition and Dietetics recommends for adults (Source: Frankenfield et al., Comparison of predictive equations for resting metabolic rate, J Am Diet Assoc, 2005).
Step 2: Pick a deficit size
| Pace | Deficit | Approx. weekly loss | Best for |
|---|---|---|---|
| Conservative | 10–15% below TDEE | 0.5 lb / week | Lean individuals, athletes protecting performance |
| Moderate | 20–25% below TDEE | 1 lb / week | Most people most of the time |
| Aggressive | 25–35% below TDEE | 1.5–2 lb / week | Higher body-fat starting points, short cuts under medical guidance |
The "1 lb of fat ≈ 3,500 calories" rule is a useful starting heuristic, but real-world results drift because metabolism adapts and NEAT drops as you eat less (Source: Hall, What is the required energy deficit per unit weight loss?, Int J Obes, 2008). Plan to re-measure, not just calculate once and forget.
Step 3: Hit a non-negotiable protein floor
Inside any deficit, the goal is to lose fat, not muscle. Protein is the single biggest dietary lever for that. A robust meta-analysis-supported floor is 0.7–1.0 g of protein per pound of body weight during a cut (Source: Helms et al., A systematic review of dietary protein during caloric restriction in resistance trained lean athletes, Int J Sport Nutr Exerc Metab, 2014).
Translation:
- 150 lb adult → 105–150 g protein/day
- 200 lb adult → 140–200 g protein/day
Set protein first, then fill the remaining calories with carbs and fats based on preference.
Get the 1-page macro cheatsheet
Step 4: Track for 14 days, then adjust
Calorie targets are an opening bid, not a verdict. Run the number for 14 days while logging daily, then look at the data:
- Lost weight at the expected rate → keep going.
- Lost faster than expected → likely water loss + glycogen drop. Hold the line for another week before changing anything.
- No change in 14 days → drop calories by ~10% or add 1,500 daily steps. Don't do both.
Common mistakes that stall weight loss
- Under-counting liquid calories. Cream, oils, dressings, and alcohol are easy to miss.
- Weekend creep. Five disciplined days erased by two unlogged ones is the most common failure pattern. Track every day for the first month.
- Cutting too hard, too fast. Big deficits crash NEAT, hunger, and adherence. The best deficit is the one you can hold for 12+ weeks.
- Ignoring strength training. Lifting 2–4x/week protects muscle while you cut. Without it, a meaningful share of "weight loss" can be lean mass.
How Fitly automates the boring parts
Once you have a target, the work is logging consistently and adjusting on cadence. Fitly handles both:
- Barcode scanner and a 5,500+ exercise database for fast workout logging.
- Weekly trend lines that flag when the scale stalls so you know when to adjust.
- Smart Coach can re-balance your plan based on real intake, not assumptions.
Get your starting target Grab the macro cheatsheet