Shelf Life & Expiration Date Calculator

Enter a manufacture date and shelf life to get the exact expiration date, days remaining, percent of shelf life left, and a 2/3-rule check for every lot. Or flip the mode and work backwards from a printed expiration date. Everything runs in your browser: no signup, up to 20 lots at once, CSV export.

What is shelf life?

Shelf life is the length of time a product stays usable and sellable, counted from its manufacture date to its expiration date. A lot made on January 15, 2026 with a 180-day shelf life expires on July 14, 2026. Knowing that date exactly, and how much of it is left, decides what you can ship.

Manufacturers set shelf life through stability testing: how long the product holds its quality, potency, or safety under normal storage. Food, beverages, supplements, cosmetics, and even fragrance oils and botanical ingredients all carry one. Once a shelf life is assigned, everything downstream is calendar math - and that math is exactly what this expiration date calculator does for you, for up to 20 lots at a time.

How to calculate an expiration date

The formula is short: expiration date = manufacture date + shelf life. The traps are in the calendar, and they are worth getting right because a one-day error can flip a lot from acceptable to rejected.

• Day-based shelf life is a straight count of days, never adjusted to month ends. January 31, 2024 plus 30 days is March 1, 2024 - it rolls straight through February.
• Month-based shelf life adds calendar months and clamps to the last day of the month when the day does not exist. January 31, 2024 plus 1 month is February 29, 2024 (leap year); January 31, 2023 plus 1 month is February 28, 2023.
• Time zones can shift a date by one day if software mixes local time into date math. This calculator does all arithmetic on calendar dates in UTC, so a lot never gains or loses a day to daylight saving time.

Worked example: a lot manufactured on January 15, 2026 with a 180-day shelf life expires on July 14, 2026, for a total shelf life of 180 days. Checked on July 17, 2026, that lot is already expired by 3 days and has 0% of its shelf life remaining.

The 2/3 rule: why retailers reject your inventory

Many retailers and distributors only accept product that arrives with at least two-thirds (66.7%) of its total shelf life remaining. It is one of the most common - and least talked about - reasons perfectly good inventory gets refused at the dock. Some buyers demand more, some less, but 2/3 is the number you will hear most often, and it is especially strict in grocery; if that is your world, our guide to inventory for food manufacturers covers the wider picture.

This calculator checks the rule with an exact whole-day comparison, not a rounded percentage: a lot passes when days remaining × 3 is at least total days × 2. That matters at the boundary. A 300-day lot with exactly 200 days left is at precisely two-thirds - it passes, even though 66.6667% would fail a naive "at least 66.7%" percentage check.

Just as useful as pass/fail is the deadline: the last day you can ship a lot and still pass is the manufacture date plus one-third of the total shelf life, rounded down. For a 365-day product, that is day 121 after manufacture - ship on day 121 and the lot arrives with 244 days (66.8%) remaining; ship a day later and it fails. The calculator shows this date for every lot, so production and shipping can plan around it instead of discovering it in a rejection email. One knock-on effect worth planning for: the 2/3 window effectively shortens how long you can hold stock, so keep buffer inventory lean - our free safety stock calculator helps you size that buffer instead of guessing it.

Best By, Use By, and Sell By: what date labels actually mean

The words in front of the date matter as much as the date itself. Under FDA date-labeling guidance, these phrases mean different things:

• Best If Used By / Best By - the date until which the product is at peak flavor or quality. Not a safety date.
• Use By - the last date recommended for use of the product at peak quality. For most foods this is still a quality date, not a safety cutoff (infant formula is the notable exception, where the date is regulated).
• Sell By - a note to the store about how long to display the product. Consumers can typically use the product safely after this date.

For a manufacturer the practical takeaway is consistency: pick one label style, apply the same shelf-life math to every lot, and make sure the date your calculator produces is the date that gets printed.

FEFO: always pick the lot that expires first

Knowing each lot's expiration date is only half the job - the other half is using the right lot first. FEFO (first-expired-first-out) means always shipping or consuming the lot with the earliest expiration date, regardless of when it arrived. A later delivery can easily carry an earlier date, which is why receipt order (FIFO) quietly fails exactly when it matters. When you check several lots at once here, the results table sorts them in FEFO order, so the lot to use next is always on top. For why FEFO beats FIFO for anything with a date, see our full guide to FEFO inventory management.

Tracking shelf life across multiple lots

One lot is easy. Twenty lots across a dozen ingredients is where spreadsheets start losing: dates live in a column nobody sorts by at pick time, quantities drift from reality, and the 2/3 deadline passes unnoticed. This calculator helps you batch-check up to 20 lots and export the results (expiration date, days remaining, percent remaining, 2/3 verdict) to CSV for your records or your buyer. If your products are built from dated ingredients, pair it with our free bill of materials template to keep component lists and costs in the same place.

But a calculator only answers the question you remember to ask. QuickBooks Online has no concept of lots or expiration dates at all - we cover that gap in our guide to QuickBooks lot tracking. Evenbatch records the lot number and expiration date the moment goods arrive, warns you before lots go out of date, and picks FEFO automatically on every order, so the dates this page computes by hand stay tracked for you - start a free trial and stop checking dates by hand.

See something outdated or incorrect on this page? Email support@evenbatch.com and we will correct it within 48 hours. Last updated: July 18, 2026.