How Many Calories does Breastfeeding Burn?
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How many calories does breastfeeding burn? The exact amount of energy used on a daily basis for lactation is still a matter of debate. These calculations should only be used as a guideline; if you find that they are not working for you, you can tweak them until they do. Not everyone is the same, we are all unique, and therefore our bodies react differently. The average lactating woman (who is breastfeeding a newborn) produces between 25 and 32 ounces of milk every 24 hours; this results in a 325 – 500 calorie deficit. Calculations are shown below. 
Energy used depends on Breastfeeding habits:
These calculations are only accurate if your baby is breastfeeding exclusively. The average metabolic rate would be different if you supplemented with formula or donor breast milk. Therefore it cannot be calculated after 6 months since most babies start solids then. 
How our Calorie Calculator Works.
Exclusive Pumpers
For those mothers who are pumping exclusively, this amount is more easily calculated. You would take the amount of milk pumped in ounces and times it by 20; this is because there are 20 calories in every ounce of breast milk. For example: if you produce 40 ounces of milk per day, the calories of the milk would be equal to 800 calories. (40 * 20 = 800)
You would then also need to take into consideration the amount of energy needed to produce that milk. Production efficiency is 80%, therefore, this would be your calculation: 40 * 20 = 800 / 0.8 = 1000. That’s a total of 1000 calories needed extra per day to produce 40 ounces of milk.
But, your metabolism is tweaked during breastfeeding, to help you use your calories more efficiently, and therefore you need fewer calories.
Once you have this amount, we need to subtract the postpartum basal metabolism (you get more out of your calories when breastfeeding). The following are average amounts.
 0 – 4 months = 300 calories
 4 months = 400 calories
 6 months and onwards = 500 calories
So for example, an exclusive pumping mother with a 3monthold baby who expresses a total of 30 ounces per day:
30 * 20 / 0.8 = 750 – 300 (basal metabolism) = 450
Therefore this mother would add an additional 450 calories to her expended calories for the day when working out how many calories she burns altogether.
Exclusive Breastfeeding Mothers
Weigh your baby before and after every feeding over a full 24 hour period. Subtract the before weight from the after feeding weight to determine how much milk your baby has taken in during each feeding. At the end of the 24 hours, add up all the amounts to determine the volume taken in during a 24 hour period. Use the same calculation above. For example: if your newborn baby drinks a total of 30 ounces daily: 30 * 20 / 0.8 = 750 calories – 300 = 450
OR a few additional examples:
If your 4monthold baby drinks 30 ounces per day:
30 (ounces of milk) * 20 (calories in milk) / 0.8 (energy to make milk) – 400 (metabolic increased rate for mother with 4monthold) = 350 (extra calories needed daily)
If your 8monthold baby drinks 32 ounces per day:
32 * 20 / 0.8 – 500 = 300
BUT
The number of calories you consume will also depend on your
1. Activity level
2. Current weight
3. Nutritional status
Most lactating women will be a little more peckish than usual; you need to listen to your body.
Work out an Average Amount
If you do not want to pump or weigh your baby to work out the exact amount of milk produced, you can use an average amount. Calculate your average amount of milk produced by converting the appropriate amount below from ml to Fluid ounces and use this in the above calculator to calculate your average amount of extra calories needed.