Quick answer
A 30 ml foundation lasts about 2-4 months with daily use (6+ months at 3-4 days a week). A 30 ml serum lasts roughly 4-12 weeks. Enter your own bottle, usage and PAO above to see exactly how long yours lasts and what it costs per application.
How to use the calculator
Pick your product, type in the bottle size in ml (1 fl oz is 29.57 ml), the price, and how you measure each use - pumps, drops, or ml directly. Add how many times a day and how many days a week you use it, plus the PAO number from the little open-jar icon. The tool returns how long the bottle lasts, total applications, cost per use, your annual spend, and a warning if it will expire before you finish it.
How long does a 30 ml foundation last?
It depends almost entirely on how much you apply. With daily wear a 30 ml bottle typically lasts 2-4 months; wearing it only 3-4 days a week pushes it past 6 months. Heavy full-face application or frequent touch-ups can burn through it in under two months.
As a rule of thumb (per application): no-makeup look about 0.3 ml, a medium pea-sized amount with a damp sponge about 0.25 ml, full coverage up to 0.5 ml, and heavy or touch-up use 1.2 ml or more (source: buycosmetics.cy, ~2026).
How long does a 30 ml serum last?
A 30 ml serum holds roughly 600 drops at about 0.05 ml each, so at 2-3 drops per use you get hundreds of applications. Once daily over the whole face, expect a minimum of 2-3 months; twice-daily use can drop a bottle to around 5 weeks (source: oreateai.com, ~2026).
How much product should you actually use per application?
Foundation (ml by coverage)
Light and natural finishes need less than you think - around 0.25 ml is plenty for most faces with a damp sponge, which also soaks up less than a brush. Switching to a damp sponge can cut foundation use by roughly 30%, directly lowering your cost per use.
Serum (drops and pumps)
Most serums are designed for 2-4 drops per application; a pea-sized 0.2 ml pump is roughly 4 drops. More is not better - excess just sits on the skin or rubs off, so dialing in the right dose is the cheapest way to make a bottle last.
The longevity and cost-per-use math
The calculator converts your per-use amount to ml, spreads it across the week, and divides the bottle by your daily rate. It then caps the answer at the PAO expiry date and flags whichever runs out first:
mlPerUse = pumps×0.2 OR drops×0.05 OR ml
mlPerDay = mlPerUse × appsPerDay × (daysPerWeek / 7)
daysUntilEmpty = bottleSize / mlPerDay
daysUntilExpiry = paoMonths × 30.44
effectiveDays = min(daysUntilEmpty, daysUntilExpiry)
costPerUse = price / (bottleSize / mlPerUse)Example: a $60, 30 ml foundation at 0.5 ml a day, 5 days a week gives about 60 applications - exactly $1.00 per use. A richer, pricier formula you apply more thinly can land cheaper per use than a budget one you slather on, which is the whole point of comparing.
Will it expire before you finish it? (PAO explained)
The open-jar symbol with a number like “12M” is the period-after-opening: how many months the product stays safe and effective after first opening. Liquid foundation is usually 6-12M and serums 3-6M (source: vivianewoodard.com, no7beauty, ~2026). If the calculator says your bottle would take longer than that to use up, you are paying for product you will throw away - a smaller size is cheaper in practice.
When a bigger bottle is NOT worth it
The per-ml price almost always drops on larger sizes, but that only pays off if you finish the bottle before its PAO expiry. For anything you use a few times a week, or a seasonal shade, the small bottle usually wins once you count the waste the calculator shows.