Eye Drop Supply Calculator
Convert bottle volume (mL) to estimated drop counts and calculate your prescription days of supply.
Ophthalmic Dispensing Details
Standard industry baseline is **20 drops/mL** for aqueous solutions (range: 15–22).
Calculated Days of Supply
Earliest Eligible Refill Date
Based on a **70%** utilization limit for your calculated 12-day supply.
Eye Drop Days of Supply Calculations: Ophthalmic Estimations
Unlike solid tablets, liquid ophthalmic preparations (eye drops) present unique compliance and auditing challenges. Insurance audit protocols require pharmacies to calculate a precise **Days of Supply** value when billing insurance claims.
Milliliters (mL) to Drops Conversion Factor
In pharmacy informatics, the standard mathematical conversion factor is **20 drops per milliliter (mL)**. Under this formula:
- A **2.5 mL** bottle contains approximately **50 drops**.
- A **5.0 mL** bottle contains approximately **100 drops**.
- A **10.0 mL** bottle contains approximately **200 drops**.
- A **15.0 mL** bottle contains approximately **300 drops**.
*Note: Actual drops per mL can vary between 15 and 22 depending on the solution's viscosity, dropper tip design, and surface tension. However, 20 is the official PBM billing benchmark.*
The Days of Supply Equation
To calculate how long an eye drop bottle will last:
For example, if you are prescribed Latanoprost 2.5 mL (50 drops total) with directions to instill 1 drop in both eyes once daily:
Days of Supply = 50 ÷ 2 = 25 Days
Under a standard 75% utilization limit, your earliest refill gate opens on **Day 19** of the 25-day cycle.
The Medicare 70% Ophthalmic Refill Rule
Self-administering ophthalmic drops can be challenging for patients, frequently leading to wastage from drops missing the eye, shaking hands, or multiple drops releasing at once. Recognizing this, the Centers for Medicare & Medicaid Services (CMS) issues specific guidance for Part D plans.
Under **CMS Chapter 5 Prescription Benefit Manual guidelines**, Medicare sponsors are strongly encouraged to set the early refill utilization gate for topical ophthalmic products to **70%** (instead of the standard 75% or 80% for oral solids).
For a 30-day supply of eye drops:
This allows patients to refill their eye drops on **Day 21** of a 30-day supply, providing a full 9-day cushion to account for wastage, spills, and administrative shipping buffers. Many states have also codified the 70% threshold into state insurance law to protect patients from running out of critical glaucoma or dry-eye therapies.