Weight Loss Calculator
Plan your weight loss journey with personalised calorie targets and timelines.
Weight Loss Planner
Why Most Weight Loss Plans Fail — and How the Maths Fixes It
Here's a stat that should bother you: roughly 80% of people who lose weight regain it within a year. Not because they lack willpower. Not because their genetics are "bad." Because they never had a plan based on actual numbers.
Weight loss isn't a mystery. It's an energy equation. If you consistently burn more calories than you eat, you lose weight. If you eat more than you burn, you gain. The hard part isn't understanding this — it's knowing your specific numbers and setting realistic expectations for how fast results should come.
That's what this calculator does. It takes your body stats, goal weight, and preferred pace, then maps out exactly how many calories to eat each day and when you'll reach your target. No guesswork. No copying someone else's plan. Just your numbers, your timeline.
The Science Behind Losing One Pound of Fat
One pound of body fat stores roughly 3,500 calories of energy (one kilogram stores about 7,700 calories). To lose that pound, you need to create a cumulative deficit of 3,500 calories — either by eating less, moving more, or both.
In practice, that means a daily deficit of 500 calories results in about 1 lb (0.45 kg) of fat loss per week. A 1,000-calorie daily deficit doubles that to roughly 2 lbs (0.9 kg) per week. Our calculator uses this relationship to project your timeline.
But there's a catch. The "3,500 calories = 1 pound" rule is a simplification. Early weight loss is faster because you also shed water and glycogen. Later weight loss slows as your body adapts. The maths gives you a solid baseline — just know that week 1 might show a 4-lb drop (mostly water), while week 6 might show only 0.5 lbs (actual fat). Both are normal.
This calculator uses the Mifflin-St Jeor equation (1990) to estimate your BMR, multiplied by your activity factor to get your TDEE. Your daily calorie target is then set based on your chosen rate of loss, with a safety floor to prevent you from eating below 80% of your BMR.
How Fast Should You Lose Weight?
Faster isn't always better. The rate at which you lose weight affects what you lose — fat, muscle, or both. Here's what the evidence says about different speeds:
| Rate | Weekly Loss | Daily Deficit | What You Lose | Best For |
|---|---|---|---|---|
| Slow | 0.25 kg / 0.5 lb | ~250 kcal | Almost entirely fat, muscle preserved | Already lean (under 20% body fat), athletes |
| Moderate | 0.5 kg / 1 lb | ~500 kcal | Mostly fat, minimal muscle loss | Most people — the sweet spot |
| Fast | 1 kg / 2 lbs | ~1,000 kcal | Mix of fat and muscle, higher adaptation risk | Significantly overweight (30%+ body fat) |
What this means for you: Unless you have a lot of weight to lose, aim for the moderate rate. Losing 1 lb per week might feel slow, but that's 52 lbs in a year — a life-changing transformation built on sustainable habits rather than suffering.
People with higher body fat (25%+ for men, 32%+ for women) can safely lose faster because their bodies have more fat reserves to draw from. As you get leaner, you need to slow down — otherwise your body starts sacrificing muscle to meet the energy gap. Check your body fat percentage to decide which rate suits you.
Why Weight Loss Stalls (The Plateau Problem)
Nearly everyone hits a plateau. You're losing weight steadily for weeks, then suddenly the scale stops moving. You haven't changed anything. What's going on?
Three things are happening at once:
1. Your Body Got Smaller
A lighter body burns fewer calories. The same 500-calorie deficit that worked at 200 lbs doesn't create the same gap at 180 lbs. Your TDEE dropped, but your calorie intake didn't. The deficit has quietly shrunk — sometimes to zero.
2. Metabolic Adaptation
Your body has downregulated non-essential processes — you fidget less, move less unconsciously, and your thyroid has slowed slightly. This "adaptive thermogenesis" can reduce your TDEE by 5–15% beyond what your new weight accounts for.
3. Water Fluctuation
Fat loss might still be happening — but water retention is masking it. Stress, sodium intake, hormonal cycles, new exercise routines, and even sleep quality can cause your body to hold 1–3 kg of extra water that hides fat loss on the scale.
How to break a plateau:
- Recalculate your TDEE using your current weight — this is step one and fixes most plateaus
- Increase daily steps to 8,000–10,000 to offset NEAT reduction
- Take a diet break — eat at maintenance for 1–2 weeks, then resume your deficit. Research shows this improves long-term adherence and reduces metabolic adaptation
- Track more carefully — weigh food with a kitchen scale for one week. Most people are surprised to find they're eating 200–400 more calories than they thought
- Add or increase strength training — muscle is metabolically expensive and keeps your BMR higher
- Wait it out — if you're consistently in a deficit, the scale will eventually catch up. Give it 2–3 weeks before making changes
How to Lose Fat Without Losing Muscle
The goal isn't just weight loss — it's fat loss. The difference matters enormously. Losing 20 lbs of pure fat leaves you leaner, stronger, and with a metabolism that's barely changed. Losing 20 lbs where half is muscle leaves you lighter but softer, weaker, and with a significantly lower BMR that makes regain almost inevitable.
Here's how to tip the ratio in your favour:
Strength Train 3–4 Times Per Week
This is non-negotiable. Resistance training sends a "keep this muscle" signal to your body. Without it, your body treats muscle as expendable during a calorie deficit. Focus on compound movements — squats, deadlifts, bench press, rows, overhead press. Use our One Rep Max Calculator to programme your weights.
Eat Enough Protein
Aim for 0.7–1g of protein per pound of body weight daily. A 2016 study in the American Journal of Clinical Nutrition found that people eating higher protein during a calorie deficit lost 27% more fat and gained 2.5 lbs of muscle compared to a lower-protein group — same calories, dramatically different results. Use our Protein Calculator to find your target.
Use a Moderate Deficit
Aggressive deficits (1,000+ cal/day) dramatically increase muscle loss. A study comparing 500 vs 1,000 calorie deficits found that the aggressive group lost significantly more muscle mass despite losing weight faster. Aim for 500 cal/day maximum, or 250 if you're already lean.
Prioritise Sleep
A University of Chicago study found that sleep-deprived dieters lost 55% more lean mass and 55% less fat than well-rested dieters on the same calorie deficit. Seven to nine hours isn't optional — it's a fat-loss requirement. Check our Sleep Calculator to optimise your schedule.
What a 500-Calorie Deficit Actually Looks Like
A 500-calorie deficit sounds abstract. Here's what it looks like in practice — both through eating less and moving more:
Cutting 500 Calories From Food
- Swap a large latte (270 cal) for a black coffee (5 cal) = 265 saved
- Skip the post-dinner biscuits (200 cal) = 200 saved
- Use spray oil instead of pouring (100 cal difference) = 100 saved
- Total: 565 calories saved without feeling deprived
Burning 500 Extra Calories
- 60-minute brisk walk = ~300 calories
- 30-minute jog at moderate pace = ~300 calories
- 45-minute weight training session = ~200 calories
- 10,000 steps throughout the day = ~400 calories
The best approach combines both. Cut 250 calories from food (easy swaps, no suffering) and burn 250 through extra activity (a 30-minute walk). This creates your 500-calorie deficit without leaving you hungry or exhausted. Check our Calories Burned Calculator to see how different activities compare.
Realistic Weight Loss Timelines
One of the biggest reasons people quit is unrealistic expectations. Here's what a healthy, sustainable timeline actually looks like for different starting points:
| Weight to Lose | Slow (0.25 kg/wk) | Moderate (0.5 kg/wk) | Fast (1 kg/wk) |
|---|---|---|---|
| 5 kg / 11 lbs | 20 weeks | 10 weeks | 5 weeks |
| 10 kg / 22 lbs | 40 weeks | 20 weeks | 10 weeks |
| 20 kg / 44 lbs | 80 weeks | 40 weeks | 20 weeks |
| 30 kg / 66 lbs | 120 weeks | 60 weeks | 30 weeks |
What this means for you: Losing 10 kg at a moderate pace takes about 5 months. That sounds like a long time — until you realise you didn't gain the weight in 5 months either. The people who succeed are the ones who accept the timeline and commit to the process, not the ones who try to shortcut it with a 6-week crash diet and end up back where they started.
These are linear estimates. Real weight loss isn't linear — you'll lose faster in the first few weeks (water and glycogen), slower in the middle (adaptation), and may have weeks where the scale doesn't budge at all. Judge progress in 4-week blocks, not daily weigh-ins.
Do Different Diets Work Better for Weight Loss?
Keto, intermittent fasting, low-carb, Mediterranean, carnivore, vegan — the diet industry is worth $250 billion, and every plan claims to be the secret. So what does the research actually show?
The largest meta-analysis ever conducted on diet comparison (published in The Lancet, 2024) looked at 121 clinical trials involving over 21,000 participants. The conclusion: all diets produce similar weight loss when calories are equal. The specific food choices matter far less than the calorie deficit.
That said, different diets help different people create that deficit. Keto works for some because cutting carbs reduces appetite. Intermittent fasting works for others because it limits eating windows. The Mediterranean diet works because it's built around filling, nutrient-dense foods.
The best diet is the one you can stick to. Pick an eating pattern that fits your lifestyle, keeps you satisfied, and lets you consistently hit the calorie target from this calculator. Use our Macro Calculator to find the protein/carb/fat split that works for your chosen approach.
7 Weight Loss Mistakes That Sabotage Your Progress
1. Not tracking liquid calories
A large Starbucks Frappuccino has 420 calories. A pint of beer: 200. A glass of orange juice: 110. Many people eat at their calorie target but drink 300–500 extra calories without logging them.
2. Weekend bingeing
A 500-calorie daily deficit Monday to Friday creates a 2,500-calorie weekly deficit. One Saturday of 1,500 extra calories (a restaurant meal + drinks + dessert) cuts that to 1,000. Consistency across all 7 days matters more than weekday perfection.
3. Cutting calories too aggressively
Eating 800 calories a day might produce fast results for 2 weeks — then your metabolism crashes, hunger becomes unbearable, and you binge. The rebound weight gain typically exceeds what you lost. A 500-calorie deficit is aggressive enough.
4. Relying only on the scale
Weight fluctuates 1–3 kg daily from water, sodium, food volume, and hormones. If you weigh yourself daily, take the weekly average and compare averages week to week. Better yet, also track waist circumference and progress photos.
5. Doing only cardio
Cardio burns calories during the session. Strength training builds muscle that burns calories 24/7. People who only do cardio during a diet lose more muscle, end up with a lower BMR, and have a harder time maintaining their weight loss long-term.
6. Not eating enough protein
Protein preserves muscle, increases satiety (you feel fuller longer), and costs the most energy to digest. Aim for 0.7–1g per pound of body weight. Most people in a calorie deficit eat far too little protein, which accelerates muscle loss.
7. Giving up after a "bad" day
One day of overeating by 1,000 calories adds about 130g (0.3 lbs) of fat. That's it. The damage is always less than you think. The real problem is when one bad day becomes "I've ruined it, I'll start again Monday" — which turns a small setback into a lost week.
When to See a Doctor About Weight Loss
A calculator and a calorie deficit are enough for most people. But see a healthcare professional if:
- You've been in a confirmed deficit for 8+ weeks with no weight change — possible thyroid, hormonal, or medication-related cause.
- You have a BMI over 40 (or 35+ with health complications) — you may qualify for medical weight management including medication or surgical options that significantly improve outcomes.
- You're experiencing disordered eating patterns — extreme restriction, binge-purge cycles, or food anxiety. A therapist specialising in eating disorders can help.
- You have diabetes, heart disease, or kidney disease — calorie restriction needs to be coordinated with medication and medical monitoring.
- You're pregnant or breastfeeding — weight loss during these periods requires specific medical guidance to ensure adequate nutrition for you and your baby.
There's no shame in getting help. GPs, dietitians, and endocrinologists have tools and tests that go far beyond what any online calculator can offer. If something feels off, get checked.
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How to use this tool
Select your preferred unit system
Enter your age, gender, height, and current weight
Enter your target weight
Common uses
- Planning a realistic weight loss timeline with a specific goal date
- Finding your daily calorie target for safe, sustainable fat loss
- Understanding how different loss rates affect your timeline
- Calculating your calorie deficit based on activity level and goals
- Comparing slow, moderate, and fast weight loss approaches
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