To calculate how long it will take to reach a weight goal starting from a given weight, on a diet that restricts the calories you eat to some number fewer than you burn every day, first subtract the weight goal from the starting weight to get the number of pounds you need to lose. Multiplying by 3500 obtains the total number of calories you need to burn from fat to reduce your weight by the desired amount. Now divide by the daily calorie shortfall anticipated in your diet plan. The result will be the number of days it should take to lose the weight. You can divide the number of days by 7 to get weeks, or by 30 for time in months.
Using the numbers from the example on page , we calculate as follows. Subtracting the weight, 145, from the initial weight, 215, gives a weight loss of 70 pounds. Multiplying this by 3500 calories/pound indicates that a total of 245000 calories of fat (whew!) will have to be burned to lose that 70 pounds. The dieter intends to reduce his daily intake by 862 calories below what he burns, so dividing this into 245000 tells us how long the diet will take: 284 days. Dividing by 7 expresses this as 41 weeks (after rounding to the nearest week); dividing by 30 gives the duration as slightly less than 9 1/2 months.