Pharmacy technician (PTCE, ExCPT)
Days supply calculators for pharmacy technicians
Enter the quantity, the units per dose and the doses a day: the days supply appears at once, rounded down. Liquids, insulin and eye drops have their own calculator further down.
Days supply of tablets or capsules
Days supply
45 days
- Units a day
- 2.00
- For 30 days
- 60 units
- For 90 days
- 180 units
Quantity divided by units a day, rounded down to whole days.
Days supply is the number of days a prescription will last if the patient takes it exactly as directed. Pharmacy technicians work it out on almost every prescription, because insurance claims require it and refills are allowed only when most of the previous supply is used. The formula is always the same: the total quantity dispensed divided by the quantity used each day. What changes from one dosage form to another is how the quantity is counted. For tablets and capsules it is a count; for oral liquids, a volume in mL, so the dose has to be in mL as well, a teaspoon being 5 mL under labeling rules; for insulin, units, found by multiplying the mL dispensed by the strength, 100 units per mL for U-100; for eye drops, an estimated number of drops per mL, since bottles are sold by volume. The result is rounded down to whole days. The calculator above handles tablets; the three below handle liquids, insulin and drops.
Questions, formats and fees by Radif Partners · Editorial policy · Method and sources
Tablets and capsules
Days supply = quantity ÷ (units per dose × doses per day). Two examples: 45 tablets at two a day give 22 days; for a 30-day supply of a capsule taken three times a day, dispense 90. The reverse question, quantity for a number of days, is asked as often as the forward one.
Oral liquids
Convert the dose to mL first, using the values federal labeling rules set (21 CFR 101.9): a teaspoon is 5 mL, a tablespoon 15 mL. Example: 150 mL of an antibiotic suspension at 2 teaspoons three times a day uses 30 mL a day, so it lasts 5 days. If the prescription is for 10 days and the bottle covers only 5, the claim and the quantity must reflect that: two bottles, not one.
Days supply of an oral liquid
Days supply
10 days
- Dose in mL
- 5.00 mL
- mL a day
- 15.00 mL
1 teaspoon = 5 mL and 1 tablespoon = 15 mL (21 CFR 101.9); days rounded down.
Insulin
Insulin is counted in units. Multiply the mL dispensed by the strength: a box of five 3 mL pens of U-100 insulin holds 15 mL, or 1,500 units. At 36 units a day that box lasts 41 days. Pens also need a small priming dose before each injection, given on the pen's label; with 32 units a day plus 4 units of priming, the same box lasts 41 days. Because pens and vials cannot be split, a box often covers more than the days written, and the claim shows the days the whole package lasts.
Days supply of insulin
Days supply
37 days
- Units dispensed
- 1,500
- Units used a day
- 40
Units in the package divided by units used a day, priming included when the label calls for it; days rounded down.
Eye drops
Eye drop bottles are sold by volume, but doses are in drops, so an estimated number of drops per mL links the two. With 20 drops per mL, a 5 mL bottle holds about 100 drops; at one drop in each eye twice a day, that is four drops a day and 25 days. Change the drops per mL to the figure your plan or the question uses, and remember to count both eyes when the sig says "OU".
Days supply of eye or ear drops
Days supply
25 days
- Drops in the bottle
- 100
- Drops a day
- 4
No federal rule fixes drops per mL; plans and exam questions state the figure, often between 15 and 20.
Common traps on exam questions
- Units that do not match. A dose in teaspoons and a bottle in mL: convert before dividing.
- Both eyes. "OU" means both eyes, which doubles the drops used.
- Ranges and "as needed". Use the highest dose and the shortest interval allowed.
- Packages that cannot be split. Inhalers, insulin pens and creams: the days supply is how long the package lasts at the directed use.
- Rounding. Round days supply down, quantities to dispense up.
Days supply sits in order entry and processing on the PTCE outline and in the dispensing process on the ExCPT test plan. For conversions and percent strength, see pharmacy math; for dose by weight, dilutions and IV rates, dosage calculations.
These calculators do exam arithmetic; they do not replace the label, the plan's rules or the pharmacist's check.