Eye Drop Supply Duration Calculator

Eye drops are expensive, and running out mid-prescription is a real problem for glaucoma patients and for anyone on steroid drops after surgery. This calculator works out how many days a bottle lasts, and, just as usefully, how much of it you are going to throw away.

The formula:

Total Drops = Bottle Volume (mL) × Drops per mL

Days Supply = Total Drops ÷ (Drops per Dose × Doses per Day × Eyes Treated)

Then the answer is capped: Usable Days = the smaller of Days Supply and 28. A preserved multi-dose bottle is discarded 28 days after you break the seal no matter how much is sloshing about inside it, so on a once-daily schedule a 10 mL bottle and a 2.5 mL bottle last exactly the same length of time. Only one of them is worth paying for.

Standard drop size: A single eye drop is approximately 0.05 mL (50 microliters). This means 1 mL of solution = about 20 drops.

Common dosing schedules:

Practical tips:

• Press on the inner corner of your eye for 1–2 minutes after instillation. This reduces drainage and increases how much medication is absorbed.
• Wait 5 minutes between different eye drops if using multiple medications.
• Eye drops typically expire 28 days after opening, regardless of how much is left. Write the open date on the carton, because nobody remembers.
• Store drops as directed. Latanoprost and a few others want refrigeration until the seal is broken.
• If you miss a dose, apply it as soon as you remember (unless it is almost time for the next dose).
• Always wash your hands before applying eye drops.

Insurance and refill timing: Most pharmacies will not refill a prescription early. Use this calculator to predict your refill date and request it 2–3 days before running out.