MariposasWeight Loss Calculator
By Zachary, builder of Mariposas · Reviewed against published exercise-science sources (references)
· Last updated June 2026
Nutrition & Calories A safe, sustainable rate.
Enter your current weight, goal and daily calorie deficit to estimate a timeline using the classic 3,500-kcal-per-pound rule. Real fat loss is not perfectly linear, expect plateaus, but it sets honest expectations.
⚕️ A general-information estimate from population-level formulas, a starting point, not a precise measurement and not medical advice.
How it works
The calculator applies the 3,500-kilocalorie-per-pound rule, a figure derived from early research by Max Wishnofsky estimating the energy stored in a pound of human adipose tissue. You enter your daily calorie deficit, and the tool divides 3,500 by that number to find how many days it takes to lose one pound, then scales that up to your total weight-loss goal. So a 500-calorie daily deficit produces roughly one pound of loss per week (3,500 divided by 500 equals 7 days), and a 250-calorie deficit doubles that timeline to about two weeks per pound. The formula is deliberately simple. It doesn't model the metabolic adaptation that happens as body weight drops, hormonal shifts, or the water weight swings that happen early in a cut, but it remains the standard starting framework because it's transparent, auditable, and close enough to reality to set useful expectations before you have your own data.
When to use it
This calculator is most useful when you're deciding on a target deficit and want to see the honest timeline before committing to it. It's also a reality check for people who have a specific date in mind, like a wedding or a race, and need to work backward to figure out whether their goal is achievable without an aggressive deficit that risks muscle loss and burnout. Coaches and trainees use it together when programming the nutrition side of a new training block.
Worked example
Say someone weighs 195 pounds and wants to reach 175 pounds, a 20-pound goal. They plan to eat at a 500-calorie daily deficit. The calculator divides 3,500 by 500 to get 7 days per pound, then multiplies 7 by 20 to land on 140 days, roughly 20 weeks or about five months. That output might surprise someone who was hoping to be done in two months. Running the numbers at a 750-calorie deficit instead would shorten the timeline to around 93 days, but the person now needs to honestly ask whether they can sustain that larger cut without losing training performance or rebounding.
Tips for an accurate result
- Use your actual measured daily intake for at least one week before picking your deficit number. Estimating from memory tends to run 20 to 30 percent low for most people, which makes the timeline prediction meaningless.
- Plug in your maintenance calories first, not an aspirational number. If you burn 2,400 calories a day and enter a 700-calorie deficit, you're planning to eat 1,700 calories. Check that number against your protein and micronutrient needs before accepting it as realistic.
- Recalculate every 10 to 15 pounds lost. Maintenance calories drop as body weight drops, so the same food intake produces a smaller deficit over time. Ignoring this is the main reason people hit plateaus and think something is broken.
- Treat the output as a midpoint estimate, not a deadline. Real loss over any given two-week window can vary by a pound or two in either direction purely from water and glycogen shifts, especially around high-carb days, hard training sessions, or hormonal cycles.
- If the timeline looks discouragingly long, resist the reflex to double the deficit. A larger cut accelerates lean mass loss and cortisol, both of which make keeping the weight off harder. A longer timeline with a moderate deficit often produces a better body composition result than an aggressive short one.
Formula & sources: methodology · references.
Now go hit the number Mariposas turns every workout, run and class into progress · collect a cute pet 🐾FAQ
- Is the 3,500-calorie-per-pound rule still accurate?
- It's a useful approximation, not a biological law. The rule holds reasonably well over short periods and for moderate deficits, but research published after Wishnofsky's original work, notably the dynamic model developed by Kevin Hall and colleagues at the NIH, shows that fat loss slows as weight drops because the body's energy expenditure adjusts downward. For planning purposes the classic rule gives you a reasonable first estimate; just expect your actual rate to be somewhat slower in the later weeks of a cut.
- Why does my weight loss seem faster in the first week?
- Early in a calorie deficit, especially if carbohydrate intake drops, the body burns through stored glycogen in the liver and muscles. Each gram of glycogen is stored with roughly 3 to 4 grams of water, so depleting those stores can produce a 3 to 5 pound drop on the scale in the first week or two that has nothing to do with fat. The calculator doesn't model this, which is why the first week often looks like you're ahead of the predicted pace.
- What deficit is too aggressive?
- There's no universal cutoff, but most sports dietitians describe deficits above 1,000 calories per day as carrying meaningful risk of lean muscle loss, particularly for people who are already reasonably lean or who are training with volume. The body will break down muscle tissue for fuel when the deficit is severe enough, which undermines body composition goals even if the scale number moves fast. Many trainees find that deficits in the 300 to 500 calorie range preserve strength and performance far better over a multi-month cut.
- Should I account for exercise calories in the deficit?
- Only if your calorie goal doesn't already include them. If you used a TDEE (total daily energy expenditure) calculator that factors in your activity level, your deficit is already baked in and you shouldn't add exercise calories on top. If you started from a sedentary base metabolic rate and then added cardio, you'd need to decide whether you're eating some of those calories back. Many people intentionally don't eat them back to steepen the deficit, which works, but changes the actual deficit the calculator is modeling.
- Can I use this calculator for very small amounts of weight, like 5 pounds?
- Yes, and it's actually more practical there. For a 5-pound goal the timeline is short enough that metabolic adaptation hasn't had time to kick in meaningfully, so the 3,500-calorie rule tracks pretty well. A 500-calorie daily deficit predicts about 35 days to lose 5 pounds. What makes small goals tricky isn't the math, it's that small changes in water weight can visually mask fat loss for weeks, so the scale can look flat even when the process is working.