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Days supply calculator

Q: How do you calculate days supply?

For tablets/capsules: Days Supply = Quantity Dispensed / (Dose per administration x Frequency per day). For example, 30 tablets taken 1 tablet twice daily = 30 / (1 x 2) = 15 days supply. For liquids: Days Supply = Volume dispensed (mL) / (Dose in mL x Frequency). For eye drops: Days Supply = (Bottles x drops per bottle) / (Drops per dose x doses per day).

Q: How do you calculate days supply for an inhaler?

Days Supply = Total actuations in inhaler / (Puffs per dose x doses per day). For example, a 200-actuation inhaler used 2 puffs twice daily = 200 / (2 x 2) = 50 days supply. Most MDI inhalers have the total number of actuations printed on the canister or labelling.

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Calculate days supply for tablets, capsules, liquids, eye drops, inhalers and insulin. Select the formulation type, enter the dispensed quantity and dosing instructions. Essential for pharmacy billing accuracy and refill scheduling.

Quantity dispensed (tablets/capsules)

Dose per administration (tablets)

Doses per day

📅 Days supply result

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Days supply in pharmacy: billing accuracy and refill timing

Days supply is the number of days a dispensed quantity will last at the prescribed dosing frequency. It determines when a patient can request a refill, drives insurance billing, and affects dispensing fee calculations for multi-month supplies.

Tablets and capsules: the straightforward formula

Days supply = quantity dispensed / (dose per administration × doses per day). 90 tablets at 1 tablet twice daily = 90 / (1 × 2) = 45 days. 90 tablets at 2 tablets once daily = 90 / (2 × 1) = 45 days. The formula is symmetric, what matters is total tablets consumed per day.

Eye drops: the most commonly miscalculated

Eye drop days supply requires knowing drops per mL (typically 20 for standard ophthalmic drops, but varies by viscosity), the number of drops per dose and how many eyes are treated. A 5mL bottle at 20 drops/mL = 100 drops total. If dosing is 1 drop in each eye twice daily = 4 drops per day. Days supply = 100 / 4 = 25 days. Many billing rejections come from incorrect eye drop days supply.

Insulin: units per package matter

A standard U-100 10mL vial contains 1000 units. A standard U-100 pen cartridge (3mL) contains 300 units. Toujeo is U-300, 3 pens contain 900 units. At 20 units daily: 3 standard pens = 900/20 = 45 days. Getting insulin days supply wrong is one of the most common pharmacy billing errors. Pair this with our SIG Code Decoder to confirm dosing instructions before calculating, and the NDC Lookup for accurate package quantity verification.

Frequently asked questions

How do you calculate days supply?

For tablets/capsules: Days Supply = Quantity / (Dose per administration x Doses per day). For liquids: Days Supply = Volume in mL / (mL per dose x doses per day). For eye drops: Days Supply = (mL x drops per mL) / (drops per dose x eyes x doses per day). For inhalers: Days Supply = (Total actuations x number of inhalers) / (puffs per dose x doses per day).

How many drops are in a 5mL eye drop bottle?

A standard ophthalmic dropper produces approximately 20 drops per mL, so a 5mL bottle contains approximately 100 drops. Drop size varies by formulation viscosity and dropper design, thicker drops (e.g. gels) produce fewer drops per mL. Use 15-20 drops per mL as a reasonable estimate for most standard eye drops.

How do you calculate days supply for an inhaler?

Days Supply = (Total actuations x number of inhalers) / (puffs per dose x doses per day). A 200-actuation inhaler used 2 puffs twice daily = 200 / (2 x 2) = 50 days supply. Most MDI inhalers print the total actuation count on the canister or outer packaging.

Formulation	Formula
Tablets	Qty / (dose × freq)
Liquid	mL / (mL × freq)
Eye drops	mL×20 / (drops×eyes×freq)
Inhaler	Acts / (puffs × freq)
Insulin	Units / (dose × freq)