Plan B Countdown Calculator
Enter when unprotected sex happened and the time right now to see how many hours have elapsed, how many hours remain inside the effective window for Plan B levonorgestrel (about 72 hours), ella ulipristal acetate (about 120 hours), or a copper IUD (about 120 hours), plus a plain status and timeline.
⏳Quick Scenario Presets
📅Timing Inputs
The calendar date the intercourse or contraceptive failure happened.
Best estimate of the clock time of the event.
Defaults to today; adjust if you are planning ahead.
Defaults to now; used to measure hours elapsed.
Each method has its own effective window and rules.
Levonorgestrel may be less effective above about 165 lb / 75 kg.
Threshold is 165 lb, equal to about 75 kg.
Vomiting soon after a pill can mean a repeat dose is needed.
Window Timeline
🔢Formula Snapshot
💊Method Windows and Typical Effectiveness
| Method | Active Ingredient | Window | Typical Efficacy | Prescription |
|---|---|---|---|---|
| Plan B One-Step | Levonorgestrel 1.5 mg | Up to 72 h | About 75-89% fewer pregnancies | No, over the counter |
| ella | Ulipristal acetate 30 mg | Up to 120 h | About 85% fewer pregnancies | Yes, prescription |
| Copper IUD (ParaGard) | Copper, non-hormonal | Up to 120 h | Over 99% effective | Yes, clinic insertion |
| Generic levonorgestrel | Levonorgestrel 1.5 mg | Up to 72 h | Same as Plan B | No, over the counter |
⏳Levonorgestrel Effectiveness by Hours Elapsed
| Hours Since Event | Tier | Relative Effect | What It Means |
|---|---|---|---|
| 0 to 24 h | Highest | Best odds | Take as soon as possible for peak benefit |
| 24 to 48 h | Strong | Good | Still clearly worthwhile, do not delay |
| 48 to 72 h | Reduced | Declining | Effect falls the closer you get to 72 h |
| Past 72 h | Window closed | Not indicated | Ask about ella or a copper IUD instead |
⚖Weight and Body Mass Considerations
| Weight Range | Levonorgestrel (Plan B) | ella (Ulipristal) | Copper IUD |
|---|---|---|---|
| Under 165 lb / 75 kg | Standard effectiveness | Effective | Most effective option |
| 165 to 195 lb / 75 to 88 kg | May be less effective | Preferred over LNG | Most effective option |
| Over 195 lb / 88 kg | Effectiveness may drop further | Effect may also decline | Not affected by weight |
📊Full Method Comparison Grid
| Method | Window Hours | Best By | Typical Efficacy | Weight Note | Prescription |
|---|---|---|---|---|---|
| Plan B One-Step | 72 h | Within 24 h | 75-89% | Weaker over 165 lb | No |
| Next Choice / generic LNG | 72 h | Within 24 h | 75-89% | Weaker over 165 lb | No |
| ella (ulipristal) | 120 h | As soon as able | About 85% | Better choice at higher weight | Yes |
| Copper IUD (ParaGard) | 120 h | As soon as able | Over 99% | Not weight dependent | Yes, insertion |
| Hormonal IUD 52 mg (LNG) | 120 h | As soon as able | Over 99% | Not weight dependent | Yes, insertion |
| Yuzpe combined pills | 72 h | Within 24 h | About 47-53% | Older backup method | Varies |
💡Practical Timing Tips
The clock: The sight of one makes you anxious; the realization that someone let down their guard. Instead of some abstract concept of time, it’s something tangible. Timing, not preparation, matter most when it comes to emergency contraception. Because it goes up against nature itself, each passing hour change your chances of success. Is there still time? Which method will work best for me? What should I do now? Will it be too late?
It could be the moment you’re standing in the drugstore aisle, staring at your smartfone screen. To do so, it employs a bit of basic math, which is meant to ease some of the anxiety around taking action. You enter the time and date when you think conception might’ve happened. It then subtracts this from now to reveal how many hours later (and therefore, how many more hours ahead) you are in the effective window for whatever method you choose.
Why Speed Matters
This shows that not all methods stays equally effective over time: Levonorgestrel pills (like Plan B) work best up to 24 hours after use, but their effectiveness drop after about 72 hours. Ulipristal acetate (ella) maintains effectiveness for up to five days. The copper IUD is highly effective during that timeframe.
A lot of folks believe that because there’s a pill designed to work for three days, it will work just as effectively after an hour as it does after seventy-one. Nope! The reference tables in the tool shows that it doesn’t. As time goes by, it becomes less effective then it was during the first hour. So yeah, if you’re two days out, you’ve got options. But you have fewer options than if you had been twelve hours out. And that’s why speed matters. Today is better than tomorrow, statistically speaking. Especially if you use levonorgestrel. Your odds go up the faster you do something about it.
These results depend heavily on body weight. For anyone who weigh more than one hundred sixty-five pounds, research indicates that the levonorgestrel is not as effective. You’ll be able to input your weight in the calculator. If it’s higher than that number, it will give you some guidance. Maybe you should of considered getting an IUD instead? Or taking ella? Those two options aren’t as impacted by body mass. It’s not just about how drug is absorbed, but also what your body does with it. Having that information in advance might help spare you a trip to clinic, where you find out too late that your method wasn’t really best for your body.
But there are practical edge cases that mess up the process. After you take the pill, maybe you throw up. You probably didn’t absorb the dose. You’ll have to take another. The tool asks for that. It prevents you from assuming coverage when you don’t have it. And it gives you presets for most common scenarios. This happens if you’re a couple of days past the event, or approaching the fifty-hour limit. Those help you visualize the timeline without having to do math yourself. This prevents guessing and lets you get help instead.
A doctor/pharmacist can never be replaced by a calculator. They see your entire medical history and how all your medications interacts. This tool will help give you perspective on how urgent your situation might be. It’ll help you determine what ways remain open. Don’t let the clock run out if it’s close. Don’t linger around waiting for something else to work after it closes if it did for one thing. Manage the clock until there isn’t any more time to manage. Time is a limited resource. Spend whatever time you have remaining wisly.
