How long does it take to lose 20 pounds?

At 1 lb/week (CDC standard): 20 weeks (~5 months). At 1.5 lb/week: ~14 weeks (~3.5 months). At 2 lb/wk: 10 weeks (~2.5 months). At 0.5 lb/wk (gentler): 40 weeks (~10 months). The actual time depends on adherence, starting weight, and metabolism. A 200-lb person with a 2,500 kcal TDEE on a 1,500 kcal diet (1,000 deficit) loses about 2 lb/wk. A 150-lb person with a 1,800 kcal TDEE on a 1,300 kcal diet (500 deficit) loses about 1 lb/wk. Our weight loss calculator personalizes the timeline based on your TDEE.

Is losing 2 pounds a week safe?

For most adults with significant weight to lose, 2 lb/wk is the upper safe limit per CDC. It requires a 1,000 kcal/day deficit, which is aggressive and hard to sustain. It works short-term (first 4-8 weeks) but often leads to plateaus, muscle loss, and metabolic adaptation. Better for: people with >50 lb to lose, those with high TDEE (active men), or short-term goals (event, vacation). Avoid long-term 2 lb/wk deficits — they cause fatigue, nutrient gaps, and rebound. Most nutritionists recommend 0.5-1 lb/wk for sustainable loss. Our weight loss calculator lets you compare rates.

What is a realistic weight loss goal per week?

0.5-1 lb per week is the most realistic and sustainable. After the first 2-3 weeks (which include rapid water loss), 1 lb/wk requires a consistent 500 kcal/day deficit. Most people can sustain 1 lb/wk indefinitely. Faster loss (>1.5 lb/wk) is possible for those with more weight to lose but is harder to maintain. The National Weight Control Registry (people who lost 30+ lb and kept it off 1+ year) shows the average rate is 1-2 lb/wk during loss, with 2,000-2,500 kcal/day maintenance afterward. Our weight loss calculator maps any rate to daily calories.

How accurate is the 3,500 kcal = 1 lb rule?

The 3,500 kcal/lb rule is an approximation. Wishnofsky (1958) derived it from observational data, and it works well for the first 10-20 lb of loss. Beyond that, metabolic adaptation kicks in — actual deficit required for continued loss is higher than the linear formula predicts. A 2011 paper by Hall et al. (Lancet) refined the model: the actual energy imbalance to lose a given amount of weight depends on starting weight, target weight, and time. The 3,500 kcal rule underestimates required deficit by 10-20% for large losses. Our weight loss calculator uses the simple formula; real-world weight loss is typically 10-15% slower than predicted.

How many calories should I eat to lose weight?

Daily calories = TDEE − deficit. For 1 lb/wk: TDEE − 500. For 1.5 lb/wk: TDEE − 750. For 2 lb/wk: TDEE − 1,000. CDC safe minimums: 1,500 kcal/day for men, 1,200 for women — never go below these without medical supervision. A 30-year-old, 5'10", 170 lb moderately active man (TDEE ~2,500) on a 500-deficit diet eats 2,000 kcal/day. A 30-year-old, 5'4", 140 lb sedentary woman (TDEE ~1,700) on a 500-deficit eats 1,200 kcal/day. Use our weight loss calculator with your specific TDEE for a personalized target.

Why is my weight loss slower than the calculator predicts?

Five common reasons: (1) water retention masking fat loss (especially during menstrual cycle or high-sodium meals); (2) muscle gain offsetting fat loss (common in new lifters); (3) metabolic adaptation (TDEE drops 5-10% as you lose weight); (4) overestimating your actual deficit (calorie tracking is 20-30% inaccurate even with good apps); (5) underestimating TDEE (activity levels, NEAT, and exercise calories are often overstated). The 3,500 kcal/lb rule is also linear — actual loss slows as you get leaner. Our weight loss calculator projects an idealized timeline; expect ~10-15% slower real-world progress.

What is a healthy weight loss rate per month?

Healthy monthly loss: 4-8 lb (1-2 lb/wk). At the high end (8 lb/month), that's a 1,000 kcal/day deficit — aggressive but tolerable short-term. At the low end (4 lb/month, or 1 lb/wk), it's the CDC standard and most sustainable. Anything slower than 2-3 lb/month is barely above normal fluctuation. For those with <20 lb to lose, 2-4 lb/month is realistic. The 2025 AHA scientific statement recommends ≥5% body weight loss as clinically meaningful, with 10-15% as the target for most health benefits. Our weight loss calculator converts any rate to daily calories and weeks to goal.

CalcCentral

Health & FitnessUpdated October 2026

Weight Loss Calculator — Weeks to Goal & Daily Calories

Pick your current weight, target weight, and weekly loss rate. Get the exact number of weeks to your goal, your daily calorie target, and milestone dates along the way.

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Updated 2026

Quick Answer: Weight Loss Timeline & Daily Calories

1 lb of body fat ≈ 3,500 kcal. Divide by 7 to get the daily deficit needed. CDC recommends 0.5–2 lb/wk for sustainable loss. Here's the math at common rates:

Weekly loss	Daily deficit	10 lb takes	25 lb takes	50 lb takes
0.5 lb/wk	250 kcal	20 wk	50 wk	100 wk
1 lb/wk	500 kcal	10 wk	25 wk	50 wk
1.5 lb/wk	750 kcal	~7 wk	~17 wk	~33 wk
2 lb/wk	1,000 kcal	5 wk	~13 wk	25 wk

Source: Wishnofsky M (1958). Caloric equivalents of gained or lost weight. Am J Clin Nutr 6(5):542-546. CDC safe minimums: 1,200 kcal/day (women) / 1,500 kcal/day (men) — never go below without medical supervision.

Weight Loss Calculator

See exactly how long it takes to reach your goal weight, what your daily calories need to be, and your milestone dates.

Units

Current weight (lb)

Target weight (lb)

Weekly loss rate (lb/wk)

Daily maintenance calories (TDEE)

Your TDEE if you ate at maintenance. Don't know it? Use the Calorie Calculator first.

Also known as: how long to lose weight calculator, weekly weight loss calculator, target weight calculator, pounds to lose calculator, weight loss timeline calculator, weight loss projection calculator, date calculator for weight loss. All use the same 3,500 kcal-per-pound-of-fat math.

Weight Loss Math

Wishnofsky M (1958). Caloric equivalents of gained or lost weight. Am J Clin Nutr 6(5):542-546. pubmed.ncbi.nlm.nih.gov
Hall KD (2008). What is the required energy deficit per unit weight loss? Int J Obes 32(3):573-576. pubmed.ncbi.nlm.nih.gov

Scientific References

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CDC — Losing Weight.

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Weight loss math: 1 lb of body fat ≈ 3,500 kcal (Wishnofsky 1958). To lose 1 lb/week, you need a 3,500 kcal/week deficit, or 500 kcal/day below your TDEE. To lose 2 lb/week, 1,000 kcal/day deficit. To lose 0.5 lb/week, 250 kcal/day. The weight loss calculator uses this formula: weeks to goal = total pounds to lose ÷ weekly rate. The math is simple but assumes consistent deficit and stable activity — actual weight fluctuates day-to-day due to water, glycogen, and food volume.

How it works

How to find the weeks and daily calories to reach your goal weight

Our weight loss calculator projects the timeline and daily calorie target to reach a goal weight based on a 3,500-kcal-per-pound deficit.

1
Enter your current and target weight
Type the weight you're at now and the weight you want to reach. The weight loss calculator accepts either pounds or kilograms.
2
Pick a weekly loss rate
Choose 0.5, 1, 1.5, or 2 lb/wk. CDC recommends 0.5–2 lb/wk for sustainable loss; 1 lb/wk is the standard for most adults.
3
Enter your TDEE
Type your daily maintenance calories (TDEE). The weight loss calculator subtracts the daily deficit (rate × 3,500 ÷ 7) from this to find your daily calorie target.
4
Read the result
The weight loss calculator shows the total weight to lose, weeks to goal, target date, daily calorie target, and four milestone checkpoints. CDC safe minimums (1,200 women / 1,500 men) are flagged if your target falls below them. The share button creates a link with your inputs pre-filled.

Weight Loss Calculator — Weeks to Goal & Daily Calories

Quick Answer: Weight Loss Timeline & Daily Calories

Weight Loss Math

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Frequently asked questions

How to find the weeks and daily calories to reach your goal weight

Enter your current and target weight

Pick a weekly loss rate

Enter your TDEE

Read the result

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