Calculate how long your prescription or OTC bottle will last.
One Eye (OD or OS)
Both Eyes (OU)
Estimated Supply Duration:
0Days
Understanding Your Eye Drop Day Supply
Managing glaucoma, chronic dry eye, or post-operative recovery requires a steady supply of medication. Knowing exactly how many days a bottle of eye drops will last is essential for planning refills and ensuring treatment continuity. Our Eye Drop Day Supply Calculator helps you estimate the lifespan of your prescription based on standard ophthalmological metrics.
How the Calculation Works
The math behind an eye drop bottle's longevity relies on three main variables: the volume of the bottle, the drop size (drops per mL), and your prescribed dosage. While different brands and viscosities vary, the pharmaceutical industry generally calculates based on a standard of 20 drops per milliliter.
The formula used is:
Total Drops = Bottle Size (mL) × Drops Per mL
Daily Usage = Number of Eyes × Drops per Eye × Daily Frequency
Days Supply = Total Drops ÷ Daily Usage
Common Eye Drop Bottle Sizes
Bottle Size (mL)
Total Drops (Est.)
Supply (1 Drop, 2 Eyes, 2x Daily)
2.5 mL
50 drops
12.5 Days
5 mL
100 drops
25 Days
10 mL
200 drops
50 Days
15 mL
300 drops
75 Days
Important Factors That Affect Supply
It is important to note that a mathematical calculation provides an ideal estimate. Real-world usage often leads to the bottle running out sooner than expected due to several factors:
Missed Drops: If a drop misses the eye or you use a second drop because you weren't sure the first one landed, your supply diminishes faster.
Solution Viscosity: Thicker drops (like gels) may result in fewer drops per mL (sometimes as low as 15 drops/mL).
Bottle Design: Some squeeze bottles are harder to control, leading to larger drops or accidental waste.
Priming: Some dispensers require "priming" which uses up a small amount of liquid before the first dose.
Practical Example
Suppose you are prescribed a 5mL bottle of drops for both eyes, to be used twice daily (1 drop per eye each time). Using the standard 20 drops per mL:
Total Drops: 5mL × 20 = 100 drops.
Daily Usage: 2 eyes × 1 drop × 2 times per day = 4 drops per day.
Supply: 100 drops ÷ 4 drops per day = 25 days.
In this scenario, if your insurance only allows a refill every 30 days, you would need to discuss the shortfall with your doctor or pharmacist to ensure you do not run out of medication.
function calculateEyeDrops() {
var bottleSize = parseFloat(document.getElementById("bottleSize").value);
var dropsPerMl = parseFloat(document.getElementById("dropsPerMl").value);
var numEyes = parseInt(document.getElementById("numEyes").value);
var dropsPerDose = parseFloat(document.getElementById("dropsPerDose").value);
var frequency = parseFloat(document.getElementById("frequency").value);
var resultContainer = document.getElementById("resultContainer");
var daysResult = document.getElementById("daysResult");
var totalDropsInfo = document.getElementById("totalDropsInfo");
if (isNaN(bottleSize) || isNaN(dropsPerMl) || isNaN(dropsPerDose) || isNaN(frequency) || bottleSize <= 0 || frequency <= 0) {
alert("Please enter valid positive numbers for all fields.");
return;
}
// Logic
var totalDropsInBottle = bottleSize * dropsPerMl;
var dailyUsage = numEyes * dropsPerDose * frequency;
var totalDays = totalDropsInBottle / dailyUsage;
// Display
daysResult.innerHTML = Math.floor(totalDays);
totalDropsInfo.innerHTML = "Total drops in bottle: ~" + Math.round(totalDropsInBottle) + "Drops used per day: " + dailyUsage;
resultContainer.style.display = "block";
resultContainer.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}