free calculator

How Long Will My Shampoo Last?

Name: How to use the Shampoo Bottle Lifespan Calculator
Uploaded: 2026-11-07
Duration: 51 s
Description: A short walkthrough showing how to find how long a bottle of shampoo or conditioner lasts and when to restock.

Find out how long a bottle of shampoo, conditioner or leave-in will last you, the date it runs out and when to restock.

How to use the How Long Will My Shampoo Last?

Choose the product and bottle size

Pick shampoo, conditioner, leave-in or another product, and enter the size printed on the label in fl oz or ml.
Set your hair length and density

They set an estimated amount per use. If you have measured one use with a spoon, type it into “Amount per use” instead.
Add how often you use it and when you opened it

Enter uses per week and the date opened. Optionally, set how many months of product you want to buy ahead.
Press Calculate

See how many uses are in the bottle, how long it lasts, the run-out date, a restock date and how many bottles cover the months you chose.
Add the restock reminder

Tap “Restock reminder” to save the restock and run-out dates to your calendar.

How to use the Shampoo Bottle Lifespan Calculator (51 s)

How long does a bottle of shampoo last? The math

How long a bottle of shampoo lasts comes down to three numbers: what is in the bottle, how much leaves it each time, and how often that happens. The calculator turns them into a count of uses and a calendar date.

uses     = bottle size ÷ amount per use   (whole uses only)
weeks    = uses ÷ uses per week
run-out  = date opened + weeks

Estimating your amount

If you have never measured a squeeze, start with our estimate for your product, hair length and density. Conditioners, masks and stylers scale with length because they coat the strands; shampoo barely does because it is worked into the scalp. Measure once with a kitchen spoon and type the real number — the field then remembers it as your measurement.

Reminders and buying ahead

The restock date is set a week before the run-out date so a new bottle arrives in time. Download the reminder and both dates land in your phone calendar. To stock up for a trip or a sale, set how many months to plan for and the tool counts the bottles.

Things the estimate cannot see

A little product always stays stuck in the bottle or pump, so the real count is usually a few uses lower.
Pumps do not always dispense the same amount every time.
If the bottle would last more than a year after opening, you will see a reminder to check its open-jar symbol.

Washes per bottle by size and amount used

Bottle	5 ml per use	10 ml per use	15 ml per use	25 ml per use
8 fl oz (237 ml)	47 uses · 24 wk	23 uses · 12 wk	15 uses · 8 wk	9 uses · 5 wk
12 fl oz (355 ml)	70 uses · 35 wk	35 uses · 18 wk	23 uses · 12 wk	14 uses · 7 wk
16 fl oz (473 ml)	94 uses · 47 wk	47 uses · 24 wk	31 uses · 16 wk	18 uses · 9 wk
33.8 fl oz (1000 ml)	199 uses · 100 wk	99 uses · 50 wk	66 uses · 33 wk	39 uses · 20 wk

Weeks assume two uses a week. 5 ml ≈ 1 teaspoon, 15 ml ≈ 1 tablespoon.

Frequently asked questions

How long does a bottle of shampoo last?

It depends on the bottle, how much you use and how often you wash. A 12 fl oz (355 ml) bottle used at about two teaspoons (10 ml) twice a week holds roughly 35 washes — around four months. Wash once a week and the same bottle lasts about eight months.

How many washes are in a 12 oz bottle of shampoo?

Roughly 70 washes at one teaspoon (5 ml), 35 at two teaspoons (10 ml) and 23 at one tablespoon (15 ml). The table on this page shows other sizes.

Why does my conditioner run out faster than my shampoo?

Shampoo mostly goes on the scalp, while conditioner has to coat every strand from roots to ends. Longer, thicker or coily hair needs noticeably more conditioner per use, so the bottle empties sooner even when the sizes match.

Do hair products expire after opening?

Yes. Many products print an open-jar symbol with a number such as “12M”, meaning it should be used within that many months of opening. Throw a product out sooner if it smells off, separates, changes color or grows anything. If a bottle would take you longer than that to finish, buy a smaller size.

How much shampoo should I buy for six months?

Multiply your uses per week by about 26 weeks, then divide by the uses in one bottle and round up. The “Plan a purchase for” field does this and shows how many bottles to buy.

Should I just buy the biggest bottle?

Big bottles are often cheaper per ounce, but only worth it if you finish them before the open-jar date. For a product you use rarely, a smaller size wastes less.