Breast milk stash calculator: When can you stop pumping?
Count your frozen bags to see how many bottle days they cover, and when the freezer could take over.
No sign-up. Your numbers stay in this browser.
Loading the calculator. If it never appears, the script did not load or JavaScript is off. The worked example below does the same sums by hand.
Keep the count without the counting
Rhythm’s stash tracker keeps a running total as you log bags and bottles.
It records the date each bag goes in, lists the oldest first, and keeps the freezer and deep freezer separate against the CDC’s 6 and 12 month limits.
A worked example
How many bottle days the freezer covers
Say the freezer holds 40 bags of 4 oz and 20 bags of 3 oz. That is 160 oz plus 60 oz, 220 oz in all. Baby has three 4 oz bottles on a daycare day, so the bottles take 12 oz of breast milk. 220 divided by 12 is 18.3, which makes 18 full bottle days. At five bottle days a week, that is three weeks and three days.
If you also pump 10 oz on each bottle day, the freezer only covers the 2 oz you don't pump. 220 divided by 2 is 110 bottle days, about 22 weeks at five a week. Stop pumping today and you are back to the first answer, 18 bottle days.
When the freezer could take over
Say you want baby on breast milk through a date 180 bottle days away. The bottles take 24 oz a day and the freezer holds 500 oz. 180 times 24 is 4,320 oz, so 3,820 oz still has to come from pumping. At 30 oz a day, that is 128 days of pumping (3,820 divided by 30, rounded up). After day 128 the freezer holds 1,268 oz, and the last 52 days need 1,248. That is the day pumping could stop.
What goes into these numbers
On each bottle day, the freezer covers the breast milk in bottles minus the milk you pump. If you pump more than the bottles take, the extra goes into the freezer. Formula bottles don't come out of the freezer.
Counting starts on the first freezer day. Milk you freeze before then is added only if you enter it in step 3. A half-pumping day is a day you pump half of what the bottles take, whatever you usually pump.
The stop date is the earliest day you could let the freezer carry every bottle day through to your date. Bottle amounts stay as you entered them, so dates are rough, and nothing is set aside for spills or leftover milk.
Tapering isn't modelled. The calculator counts pumping at the level you enter until the stop date, then none. Storage time isn't part of the math either; use current CDC storage guidance for what is safe to use.
Questions
How much of a breastmilk stash should I have?
There is no single number. It depends on how many bottle days you need to cover and how much of each day's milk you pump. Someone who pumps close to what the bottles take needs a small stash; someone who pumps nothing on bottle days needs enough for every one of them. Enter your own bags and bottles in the calculator and it shows how many bottle days your freezer covers, with no target attached.
How long will 500 ounces of breastmilk last?
It depends on how much baby drinks from the freezer each day. Divide 500 by that amount: at 12 oz a day it is 41 full days, at 24 oz a day it is 20, and at 30 oz a day it is 16. If you pump on those days, only the difference comes out of the freezer. With 24 oz in bottles a day and 20 oz pumped, the freezer covers 4 oz a day, and 500 divided by 4 is 125 days.
When can I stop pumping?
In the freezer-stash sense, when the freezer holds enough to cover every bottle day up to the date you want baby on breast milk. Turn on "When can I stop pumping?" in the calculator and give it a date, or baby's birthday and an age. It shows the day pumping could end. If the milk won't reach that far, it shows the date it does reach and how much more you would pump each bottle day to get there. Tapering isn't modelled, and dropping a night or daytime session is a supply question for a lactation consultant.
Do formula bottles use up the freezer?
No. Count them in the bottle total as formula bottles and the calculator keeps them out of the math. It only counts the breast milk you enter.
Does it allow for spills, leftover milk, or growth spurts?
No. Bottles stay at the amount you enter, so the dates are rough. Babies drink more as they grow, and an unfinished bottle isn't budgeted for. Change the bottle size and the dates move.
Are my numbers saved anywhere?
Only in this browser, in local storage on this device, so clearing site data clears them. They are never sent to a server. The site counts anonymous page visits, and your numbers are not part of that.
Last updated: October 2026
Rhythm records when each bag went into the freezer and lists the oldest first when you take one out. See the milk stash tracker.