"How long will it take to lose 10 pounds?" The answer mostly comes down to one thing: how many calories you cut each day. This page estimates the time the same way the Diet Diary game does.
The math
A kilogram of body fat is worth about 7,200 kcal (body fat is roughly 80% fat, and each gram of fat holds about 9 kcal). That's about 3,300 kcal per pound. Multiply the weight you want to lose by that number, then divide by your daily calorie cut, and you get the number of days.
Days = pounds to lose × 3,266 ÷ daily calorie cut (kcal)Example: losing 10 lb with a 500 kcal daily cut
10 × 3,266 ÷ 500 = about 65 days (about 2.1 months)
Your daily calorie cut is the gap between the calories you burn (resting metabolism × activity level + exercise) and the calories you eat. How the math works explains how calories burned are worked out.
Chart: weight to lose vs. daily calorie cut
Estimates from the formula above (one month = 30.4 days).
| Weight to lose | −200 kcal/day | −300 kcal/day | −500 kcal/day | −700 kcal/day |
|---|---|---|---|---|
| 5 lb | about 2.7 months82 days | about 8 weeks54 days | about 5 weeks33 days | about 3 weeks23 days |
| 10 lb | about 5.4 months163 days | about 3.6 months109 days | about 2.1 months65 days | about 7 weeks47 days |
| 15 lb | about 8.0 months245 days | about 5.4 months163 days | about 3.2 months98 days | about 2.3 months70 days |
| 20 lb | about 10.7 months327 days | about 7.2 months218 days | about 4.3 months131 days | about 3.1 months93 days |
| 30 lb | about 16.1 months490 days | about 10.7 months327 days | about 6.4 months196 days | about 4.6 months140 days |
| 40 lb | about 21.5 months653 days | about 14.3 months435 days | about 8.6 months261 days | about 6.1 months187 days |
| 50 lb | about 26.8 months816 days | about 17.9 months544 days | about 10.7 months327 days | about 7.7 months233 days |
Why it usually takes a bit longer than the chart
As you lose weight, your resting metabolism drops too. And if you keep eating far less than you burn, your body starts saving energy and burns less (metabolic adaptation). So even on the same diet, your daily calorie cut slowly shrinks, and it takes longer than the chart says.
Using the same math as Diet Diary, here's how long it takes the example man from How the math works (35 years old, 5'9", 200 lb, on-the-go job) to lose 20 lb if he eats a fixed amount below what he burned on day one (no exercise, muscle, or scale ups and downs included):
| Eating plan | Simple math | Same math as the game |
|---|---|---|
| Eat 500 kcal less than you burned on day one | 131 days | 151 days |
| Eat 700 kcal less than you burned on day one | 93 days | 123 days |
Cutting 700 kcal a day gets there sooner, but because his daily balance stays below −500 kcal, metabolic adaptation kicks in and the gap from the simple math grows. A pace you can keep up tends to land closer to the numbers.
Calculator
This is the simple math. As explained above, real progress usually takes a little longer.
Losing weight without overdoing it
- The game warns you when a day's eating drops below 1,200 kcal. Skipping meals day after day tends to slow your metabolism and makes it easier to regain weight
- Pick a goal weight that keeps your BMI at 18.5 or above. The game won't let you set a goal below that
- The number on the scale can swing by a pound or so a day from water. Watch the trend over one or two weeks instead of day to day
These numbers are estimates, and real results vary with your body and lifestyle. Talk to a doctor or registered dietitian before starting a real weight-loss plan.
Try it in the game
Diet Diary is a free browser game where you choose meals, exercise and sleep each day to guide a pixel-art character to a goal weight. It uses this same math, so you can watch the weight change one day at a time.