HAIR PRODUCT OPENING AND COST RECORD
Price estimates do not establish suitability or shelf life.

PRODUCT / VERSION / REGION:
BATCH / LOT / LABEL SOURCE:
PURCHASE DATE:
FIRST OPENED (or unknown):
PRINTED DATE:
OPENING PERIOD:
STORAGE INSTRUCTIONS / UNKNOWN HISTORY:
PRICE AND CURRENCY:
PACK QUANTITY AND UNIT:
QUANTITY PER USE, SAME UNIT:
UNUSED QUANTITY, SAME UNIT:
OBSERVED OR ASSUMED INPUTS:
ACTUAL COMPLETED USES:
QUESTION FOR THE MAKER:

FORMULAS
quantity used = pack quantity - unused quantity
equivalent uses = quantity used / quantity per use
estimated purchase cost per use = full purchase price / equivalent uses
realized purchase cost per completed use = full purchase price / actual completed uses

HYPOTHETICAL EXAMPLES
Small hypothetical bottle | $9 / 200 mL | 4 mL | 50 | $0.18
Large hypothetical bottle; all used | $15 / 400 mL | 4 mL | 100 | $0.15
Same large bottle; 200 mL not used | $15 / 200 mL actually used | 4 mL | 50 | $0.30
Hypothetical mask jar | $20 / 100 g | 2 g | 50 | $0.40

LABEL TYPES
Period after opening | Open-jar symbol with a period such as 12M | Record first-opened date; follow the actual stated period and storage directions.
Minimum-durability date | A date, “best used before the end of,” or the associated symbol | Copy the actual date and any required storage conditions.
Batch / lot reference | An identifier such as a printed letter-number code | Keep it for manufacturer identification; do not assume it is a date you can decode.
Unopened shelf-life statement | Manufacturer’s statement for a named product | Check the stated starting point; do not automatically add years to purchase date.

CHECKED MANUFACTURER EXAMPLE
Named Garnier FAQ: 3 years unopened, 12 months opened.
Unopened clock start is not specified in that answer.
Do not add 3 years to purchase date or generalize to other products.

PRACTICE CASES AND ANSWERS

1. A $15 / 400 mL bottle costs less per mL than a $9 / 200 mL bottle. You use only 200 mL of the large bottle before it must be discarded. With 4 mL per recorded use, which has the lower purchase cost per use?
Answer: The small bottle: $0.18 per use versus $0.30 for the large bottle.
Both supply 50 recorded uses in this example. Divide the full purchase price by those uses: 9/50 and 15/50. A lower package-unit price did not prevent unused product from raising the realized cost.

2. A mask is labelled 100 g and a conditioner 250 mL. Can their pack quantities be compared directly as if a gram equals a millilitre?
Answer: No. Keep the quantity and use amount in the same unit for each product.
Mass and volume are different quantities. A density or manufacturer-specific conversion would be needed to convert between them. You can compare resulting currency-per-use estimates after calculating each with its own compatible units.

3. A hypothetical product’s actual label says 6M after opening. You first open it on 20 March 2026. Which date belongs in the six-month reminder?
Answer: 20 September 2026, subject to the actual product instructions and conditions.
The period is measured from opening, not purchase. This is a calendar illustration, not the verified period for a named product. A reminder does not override an earlier printed date, compromised storage or other reasons to stop use.

4. A U.S. cosmetic has no printed expiration date. Does that mean it stays usable indefinitely?
Answer: No. The absence of a mandatory cosmetic date is not unlimited shelf life.
FDA says U.S. cosmetics are not required to carry specific shelf lives or expiration dates, while manufacturers remain responsible for safety. Product type, use and storage still matter. Ask the maker about the named product instead of inventing a universal period.

5. The checked Garnier FAQ says 3 years unopened and 12 months opened. Can you write “expires 3 years after I bought it” on every bottle?
Answer: No. The FAQ does not establish that purchase date is the unopened clock’s starting point.
Keep the statement tied to the named product. Consult the actual packaging and maker if the batch age or starting point is unclear. Do not extend that FAQ answer to another formula, brand, region or repacked container.

6. A product is beyond its stated limit but still smells normal. Can smell alone renew that limit?
Answer: No. Normal smell does not replace the label or establish safety.
FDA describes several ways cosmetics can change or become contaminated. Some problems are not settled by a casual smell check. Do not use a reassuring appearance to extend a stated period or date.

7. A partly used bottle has an unreadable opening date and no dependable record. Should you choose today as a new opening date?
Answer: No. Leave the date unknown rather than resetting the clock.
Save the available label and batch details and ask the manufacturer about the unresolved history. Adding a fresh reminder to an already-opened product would hide information instead of establishing a new safe period.

8. You enter 200 units purchased and 200 units not used in the cost calculator. Should it report zero cost per use?
Answer: No. There is no positive used quantity to divide into uses.
The estimate must remain unavailable. Zero completed use does not erase the purchase expense, and division by zero does not produce a meaningful per-use price. Record the unused purchase separately.