Determine your eligibility window and effectiveness based on time elapsed.
Weight impacts pill effectiveness.
Levonorgestrel (Plan B One-Step, Take Action, etc.)
Ulipristal Acetate (Ella)
Copper IUD (Paragard)
Hormonal IUD (Mirena, Liletta)
Time Analysis & Recommendation
Time Elapsed
0 hrs 0 mins
Window Remaining
0 hrs 0 mins
Efficacy Status
—
* This calculator provides estimates based on standard medical guidelines. Every body is different. Please consult a pharmacist, doctor, or clinic immediately for medical advice.
// Set default date to today
var today = new Date();
var dd = String(today.getDate()).padStart(2, '0');
var mm = String(today.getMonth() + 1).padStart(2, '0'); //January is 0!
var yyyy = today.getFullYear();
document.getElementById('incidentDate').value = yyyy + '-' + mm + '-' + dd;
// Set default time to roughly now
var hours = String(today.getHours()).padStart(2, '0');
var mins = String(today.getMinutes()).padStart(2, '0');
document.getElementById('incidentTime').value = hours + ':' + mins;
function calculateEC() {
var dateInput = document.getElementById('incidentDate').value;
var timeInput = document.getElementById('incidentTime').value;
var weightInput = parseFloat(document.getElementById('weightLbs').value);
var method = document.getElementById('ecMethod').value;
var resultDiv = document.getElementById('resultDisplay');
if (!dateInput || !timeInput) {
alert("Please enter both the date and time of unprotected sex.");
return;
}
var incidentDateTime = new Date(dateInput + 'T' + timeInput);
var now = new Date();
// Calculate difference in milliseconds
var diffMs = now – incidentDateTime;
if (diffMs 0) {
var remH = Math.floor(remainingHoursTotal);
var remM = Math.floor((remainingHoursTotal – remH) * 60);
displayRemaining = remH + " hrs " + remM + " mins";
// Efficacy Status Logic
if (method === 'levonorgestrel') {
if (elapsedHours < 24) {
statusText = "Highest Efficacy (95%)";
statusClass = "ec-success";
} else if (elapsedHours 165) {
showWeightWarning = true;
weightMsg = "Warning: Levonorgestrel (Plan B) may be less effective for individuals weighing over 165 lbs (75 kg). Consideration of Ella or an IUD is strongly recommended.";
if (weightInput > 175) {
weightMsg = "Critical: Clinical studies suggest Levonorgestrel may not be effective for weights over 175 lbs. Please consult a doctor about Ulipristal Acetate (Ella) or an IUD immediately.";
statusText = "Low Efficacy Likely due to Weight";
statusClass = "ec-danger";
}
}
} else if (method === 'ulipristal') {
if (weightInput > 195) {
showWeightWarning = true;
weightMsg = "Warning: Ulipristal Acetate (Ella) may be less effective for individuals weighing over 195 lbs (88 kg). A Copper IUD is the recommended option for this weight range.";
}
}
}
// Update DOM
document.getElementById('timeElapsedVal').innerText = elapsedHours + " hrs " + elapsedMinutes + " mins";
document.getElementById('windowRemainingVal').innerText = displayRemaining;
var statusEl = document.getElementById('efficacyStatus');
statusEl.innerText = statusText;
statusEl.className = "ec-metric-value"; // reset
// Apply color based on status
if(statusClass === 'ec-success') statusEl.style.color = "#155724";
if(statusClass === 'ec-warning') statusEl.style.color = "#856404";
if(statusClass === 'ec-danger') statusEl.style.color = "#721c24";
var weightDiv = document.getElementById('weightWarning');
if (showWeightWarning) {
weightDiv.innerHTML = weightMsg;
weightDiv.style.display = 'block';
} else {
weightDiv.style.display = 'none';
}
// Recommendation Text
var finalRec = "";
if (remainingHoursTotal < 0) {
finalRec = "You have passed the standard window for " + method + ". However, do not give up. Consult a healthcare provider immediately as IUDs can sometimes be inserted slightly later depending on ovulation timing.";
} else {
if (method === 'levonorgestrel') {
finalRec = "Take the pill as soon as possible. Effectiveness decreases as time passes.";
} else if (method === 'ulipristal') {
finalRec = "Ella requires a prescription. Contact a doctor or pharmacy immediately. It maintains consistent effectiveness up to 120 hours.";
} else {
finalRec = "Contact a clinic immediately to schedule insertion. The IUD is the most effective form of emergency contraception (over 99%).";
}
}
document.getElementById('recommendationText').innerHTML = finalRec;
// Show Results
resultDiv.style.display = "block";
resultDiv.scrollIntoView({behavior: "smooth"});
}
Understanding Your Emergency Contraception Window
Time is the most critical factor when it comes to emergency contraception (EC). The sooner you act after unprotected intercourse, the higher the likelihood of preventing pregnancy. This calculator helps you determine exactly how much time has passed and which method may be most appropriate for your specific timeline and body metrics.
The 3 Main Types of Emergency Contraception
1. Levonorgestrel Pills (Plan B One-Step, Take Action, My Way)
Often referred to as the "morning-after pill," these are available over-the-counter without a prescription. While the FDA labeling states they are effective for up to 72 hours (3 days), clinical research suggests they work best if taken within the first 24 hours. The effectiveness drops significantly with every passing day.
Best for: Immediate use (0-24 hours).
Availability: Over-the-counter.
Weight Limit: Effectiveness may decrease for individuals over 165 lbs (75 kg).
2. Ulipristal Acetate (Ella)
Ella is a prescription-only pill that is more effective than Levonorgestrel. A key advantage of Ella is that its efficacy does not decrease over time; it is just as effective on day 5 as it is on day 1. It works by delaying ovulation even if your body is just about to release an egg.
Best for: Days 0-5 (up to 120 hours).
Availability: Prescription required.
Weight Limit: Effectiveness may decrease for individuals over 195 lbs (88 kg).
3. Copper IUD (Paragard) and Hormonal IUDs (Mirena, Liletta)
The most effective form of emergency contraception is the insertion of an Intrauterine Device (IUD) by a healthcare professional. It is more than 99% effective and can be used up to 5 days after unprotected sex. Unlike pills, the IUD's effectiveness is not impacted by body weight.
Best for: Highest efficacy guarantee; long-term birth control needs.
Availability: Doctor's appointment required.
Weight Limit: None. Effective for all weights.
Why Weight Matters
Many people are unaware that body weight significantly influences the effectiveness of oral emergency contraceptives. Studies have shown that Levonorgestrel (Plan B) begins to lose effectiveness in women weighing over 165 lbs and may be ineffective for those over 175 lbs. In these cases, Ulipristal Acetate (Ella) or an IUD are strongly recommended to ensure pregnancy prevention.
When to Take a Pregnancy Test
Emergency contraception is not 100% effective. If your period is more than a week late, or if you experience severe lower abdominal pain (which could indicate an ectopic pregnancy), take a pregnancy test and consult a healthcare provider. Generally, you should take a test 3 weeks after the unprotected incident if your period has not arrived.
Frequently Asked Questions
Can I take Plan B after 72 hours?
While the label says 72 hours, some studies suggest there is still some benefit up to 120 hours, though it is much weaker. Ella or an IUD are much better options after day 3.
Does EC cause an abortion?
No. Emergency contraception prevents pregnancy by delaying ovulation or preventing fertilization. It does not terminate an existing pregnancy.