Weight Loss Calculator
Estimate how long it takes to go from your current weight to a goal weight at a chosen daily calorie deficit.
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What this tool does
Estimate how long it takes to go from your current weight to a goal weight at a chosen daily calorie deficit. The 3,500 kcal/lb rule is a rough planning heuristic — real trajectories are slower and non-linear as maintenance calories fall with weight. This tool does not set a deficit for you or judge whether a goal weight is appropriate.
How to use the Weight Loss Calculator
- Enter or select current weight in lb.
- Enter or select goal weight in lb.
- Enter or select daily calorie deficit (kcal).
- Read the calculated result; change any measurement to compare alternatives.
Formula
days = pounds to lose × 3,500 / daily deficit (3,500 kcal-per-pound rule of thumb, labelled)
- current
- Current weight (lb, before metric conversion)
- goal
- Goal weight (lb, before metric conversion)
- deficit
- Daily calorie deficit (kcal)
The 3,500 kcal/lb rule is a rough planning heuristic — real trajectories are slower and non-linear as maintenance calories fall with weight. This tool does not set a deficit for you or judge whether a goal weight is appropriate.
Worked example
For weight loss calculator, the following measurements illustrate the exact method: Current weight: 200; Goal weight: 180; Daily calorie deficit (kcal): 500.
Inputs
- Current weight200 lb
- Goal weight180 lb
- Daily calorie deficit (kcal)500
Result
- Estimated days140
- Estimated weeks20
- Pounds to lose20 lb
Results explained
- Estimated days
- Estimated days from the formula above. The 3,500 kcal/lb rule is a rough planning heuristic — real trajectories are slower and non-linear as maintenance calories fall with weight. This tool does not set a deficit for you or judge whether a goal weight is appropriate.
- Estimated weeks
- Estimated weeks from the formula above. The 3,500 kcal/lb rule is a rough planning heuristic — real trajectories are slower and non-linear as maintenance calories fall with weight. This tool does not set a deficit for you or judge whether a goal weight is appropriate.
- Pounds to lose
- Pounds to lose from the formula above, expressed in lb before metric conversion. The 3,500 kcal/lb rule is a rough planning heuristic — real trajectories are slower and non-linear as maintenance calories fall with weight. This tool does not set a deficit for you or judge whether a goal weight is appropriate.
Frequently asked questions
At a 500 kcal/day deficit, the rule-of-thumb arithmetic gives 20 × 3,500 ÷ 500 = 140 days (20 weeks). Real-world timelines usually run longer — see the note on the 3,500 rule.
A pound of body fat stores roughly 3,500 kcal, so a cumulative deficit of that size approximates a pound lost. It ignores water shifts and metabolic adaptation, so projections are optimistic and approximate.
A lighter body has lower maintenance calories, so the same intake creates a smaller deficit; activity and appetite also adapt. Re-checking your deficit calculator numbers at each 10 lb lost keeps projections honest.
Common planning deficits are 250–1,000 kcal/day (about 0.5–2 lb/week by the rule of thumb). This tool does not choose for you — larger deficits and any medical conditions warrant professional guidance.
No. It is straight-line arithmetic from a heuristic. Illness, adherence, water retention and adaptation all move real dates; use it for planning ranges, not deadlines.