Plan B Calculator

Accidents and missed pills happen, and the clock starts ticking immediately. Plan B is an emergency contraception pill containing levonorgestrel. Its estimated effectiveness depends heavily on how soon it is taken. This Plan B Calculator shows which timing band you are in. Enter the hours since unprotected sex to see the estimate. An optional weight entry adds a note that may matter.

Please read this page as education, not medical advice. Emergency contraception is time-sensitive, so do not let reading replace acting. A pharmacist or clinician can advise you today, in person. If you are within the window, sooner is genuinely better. The sections below explain why timing matters so much.

The estimate cannot see your cycle, your medicines, or your history. Only a professional conversation covers those. Use the number here to understand urgency, nothing more. Then make the call or the trip straight away. Information should speed you up, never slow you down.

What Is Plan B and How Does It Work?

Plan B is a single pill with a larger dose of levonorgestrel. That hormone also appears in many daily birth control pills. The emergency dose works mainly by delaying ovulation. If no egg is released, fertilisation cannot happen. It may also thicken cervical mucus slightly.

The pill works before pregnancy begins. It does not end an established pregnancy. It is not the abortion pill, which is a different medicine entirely. Once implantation has happened, levonorgestrel has no effect. That is why the timing window matters so much.

Pharmacies stock it widely, often without a prescription. Rules differ between countries and regions. Staff can explain the local rules in minutes. Cost also varies, and some clinics supply it free. Asking early gives you the most options.

Brand and generic versions contain the same active ingredient. Generics usually cost noticeably less. Pharmacists can point you to whichever is in stock. Some places ask for identification or an age check. Others hand it over at the counter without fuss. Either way, the conversation stays routine for staff.

Why Timing Changes Everything

Effectiveness falls as hours pass. Taken within the first day, the pill prevents roughly 95 percent of expected pregnancies in published estimates. Between one and two days, the figure drops to about 85 percent. Between two and three days, it falls to about 58 percent.

Those numbers are population estimates, not personal promises. Studies measured groups, and individual situations vary. Body weight, cycle timing, and other medicines can all play a part. Treat each figure as a guide to urgency. The clear message is that earlier beats later.

After 72 hours the picture changes sharply. Some use continues up to 120 hours, but the pill is much weaker there. A rough estimate near 30 percent is sometimes quoted. Other options usually work better in that window. A clinician can explain them the same day.

The underlying biology explains the rush. Sperm can survive inside the body for up to about five days. An egg survives for roughly a day after release. Delaying ovulation keeps the two from ever meeting. Once they meet, this pill has nothing left to prevent. That single fact drives every timing band.

How to Use the Plan B Calculator

Two entries produce your timing estimate.

1. Count the hours since the unprotected sex happened.
2. Enter that number, using half hours if needed.
3. Add your body weight in pounds if you wish.
4. Press the blue Calculate button to see the estimate.
5. Read the effectiveness band and the hours left in the main window.
6. Contact a pharmacist or clinician promptly for personal advice.

Guessing the hours roughly is fine. Round toward the larger number if unsure. A cautious estimate beats an optimistic one here. The weight entry stays optional and changes only the extra note. Nothing you enter gets stored or sent anywhere. The estimate appears on this page alone. Close the tab and the entries vanish with it.

Worked Example 1: Ten Hours Afterwards

The Inputs

Imagine a condom broke late last night. About ten hours have passed since then. The person has not entered a body weight. Those details go into the calculator as they stand.

The Calculation

Ten hours sits inside the first band. The first band covers hours zero to twenty-four. Published estimates put effectiveness near 95 percent there. The main 72-hour window still has 62 hours left. No weight note appears, since no weight was entered.

The Result

The estimate shows about 95 percent effectiveness. Even so, waiting would only weaken it. The sensible move is taking the pill now, not tonight. A pharmacist can confirm suitability in minutes. This example shows the strongest possible timing position. It also shows why guessing hours honestly matters.

Worked Example 2: Sixty Hours Afterwards, With a Weight Note

The Inputs

Now imagine a missed pill discovered much later. Sixty hours have passed since unprotected sex. This person enters a body weight of 180 pounds. Both entries go into the calculator.

The Calculation

Sixty hours falls in the third band, from 48 to 72 hours. Effectiveness there is estimated near 58 percent. Only twelve hours remain in the main window. The weight also passes 165 pounds. That triggers the extra weight note in the result.

The Result

The estimate shows about 58 percent, plus the weight note. Evidence suggests the pill may work less well above roughly 165 pounds. It still works for many people, though. A clinician might suggest a more reliable option instead. Acting today matters far more than debating the estimate. Twelve remaining hours leave no room for a wait-and-see weekend.

Options Beyond the 72-Hour Window

Passing 72 hours does not end the conversation. A copper IUD is the most effective emergency option. A clinician can fit one within five days of unprotected sex. It then keeps working as ongoing contraception for years. Many people never hear about this route in time.

A prescription emergency pill also exists for the later window. It stays effective for up to five days. Availability depends on local rules and prescribers. A pharmacist can point you to the fastest route. Speed still matters, even in this window.

Beyond five days, emergency options run out. A pregnancy test becomes the next step if a period is late. Clinics can test earlier than home kits sometimes. Support services can talk through any outcome. You do not have to navigate that alone.

Uncertainty about the exact hour is common. Do not let it stall you. Staff would rather see you at hour seventy than hear about hour ninety. They work with estimates every day. Give them your best honest count and let them advise from there.

Body Weight and Effectiveness: What Is Known

Research suggests body weight may affect this pill. Studies found higher pregnancy rates among heavier users. The signal becomes noticeable around 165 pounds, roughly 75 kilograms. Regulators reviewed the data and kept the product available. Guidance still describes it as an option for everyone.

Weight is one factor among several. Cycle timing near ovulation matters greatly too. Other medicines, like some seizure or tuberculosis drugs, can interfere. Herbal products such as St John’s Wort may also reduce effect. Mention everything you take when asking for advice.

The calculator’s weight note is a prompt, not a verdict. It simply flags when a conversation matters most. A clinician might recommend the copper IUD instead. That option does not lose strength with body weight. Knowing this in advance saves precious hours.

Studies phrase the threshold in different ways. Some use total body weight, others use body mass index. The 165 pound line is the commonly cited marker from the weight research. Nobody should read it as a cliff edge. Effectiveness likely fades gradually rather than switching off.

Common Myths That Cause Harmful Delays

Myths slow people down at the worst moment. One claims the pill harms future fertility. Evidence shows fertility returns quickly after use. Another myth says it works for the whole cycle. It covers only the act before it, nothing later.

Some people believe two pills work twice as well. Doubling the dose does not double protection. It mainly raises the chance of nausea. Others assume a prescription is always required. Many regions allow direct pharmacy sale instead. Checking the real rule takes one phone call.

Embarrassment causes the longest delays of all. Pharmacy staff treat these requests as ordinary healthcare. They will not lecture or judge you. Walking in early protects your options. Walking in late protects nothing at all.

What to Expect After Taking It

Most side effects are mild and brief. Nausea is the commonest complaint. Headaches, tiredness, and breast tenderness also occur. Dizziness sometimes follows for a few hours. Eating a small snack with the pill can help some people. Rest usually settles the rest.

Your next period may shift slightly. It can arrive a few days early or late. Flow may be lighter or heavier than usual. Spotting between periods happens occasionally too. These changes usually settle by the following cycle. Persistent disruption deserves a clinic conversation.

Warning signs are rare but important. Severe abdominal pain needs prompt medical attention. So does very heavy bleeding or fainting. A pregnancy test remains wise if your period is over a week late. Keep the pharmacy’s number saved until the cycle resolves.

Keeping perspective helps during the wait. Most people feel normal again within a day. Waiting for the next period is usually the hardest part. Marking the expected date reduces the daily guessing. Then let the test, not anxiety, deliver the answer.

Tips for Acting Quickly and Safely

1. Act today rather than waiting for tomorrow morning.
2. Call the pharmacy ahead to confirm stock.
3. Mention every medicine and supplement you currently take.
4. Ask about the copper IUD if you are near 72 hours.
5. Use condoms for any further sex this cycle.
6. Take a pregnancy test if your period is over a week late.
7. Book a sexual health check for infections as well.

Keep the tone practical, not panicked. Pharmacists answer these questions daily. Nothing about asking will surprise them. Clear information beats rumours from friends or forums. Write down the hour of the incident before you forget it. That small note sharpens every later conversation. It also anchors the estimate shown by the calculator above.

Frequently Asked Questions

General Questions

1. What exactly is the Plan B pill?

It is a single emergency contraception pill containing levonorgestrel. People take it after unprotected sex or contraception failure. It works mainly by delaying ovulation, so fertilisation cannot occur. It is sold under several brand and generic names in pharmacies.

2. Is this calculator giving me medical advice?

No, this page is educational only. It explains published timing estimates in plain language. Your situation may involve factors the tool cannot see. A pharmacist, clinician, or sexual health service can advise you personally. Reach one today if you need this pill.

3. How quickly should the pill be taken?

As soon as possible is the standard guidance. It works best within the first 24 hours. Effectiveness remains reasonable up to 72 hours, then drops. Do not wait for a perfect moment. Taking it now beats taking it slightly later.

4. Does the pill end an existing pregnancy?

No, it does not. Levonorgestrel works before pregnancy is established, chiefly by delaying ovulation. It cannot disrupt an implanted pregnancy. The abortion pill is a completely different medicine. Confusing the two causes needless worry for many people.

5. Where can I get emergency contraception?

Pharmacies are the usual first stop. Many sell it without a prescription, though rules vary by country. Clinics and sexual health services also supply it, sometimes free. Calling ahead confirms stock and opening hours. That call can save a wasted journey.

How the Calculation Works

6. Why does timing change the estimate so much?

The pill must act before ovulation happens. Each passing hour raises the chance that ovulation has already occurred. Once an egg is released and fertilised, the pill cannot help. Published studies therefore show falling success as delays grow.

7. What does the 95 percent figure actually mean?

It means studies estimated about 95 percent of expected pregnancies were prevented. Researchers compare pregnancies observed against pregnancies expected without treatment. It is not a personal guarantee for any individual. Your odds depend on cycle timing and other factors.

8. Why does the main window end at 72 hours?

The product was studied and licensed mainly for use within three days. Evidence of benefit shrinks quickly after that point. Some guidance allows consideration up to 120 hours, with low expectations. The 72-hour line reflects the evidence, not a cliff edge.

9. What happens between 72 and 120 hours?

The pill becomes much less reliable there. A rough estimate around 30 percent is sometimes quoted, with wide uncertainty. A copper IUD works far better in this window. One prescription option also remains effective. Speak to a clinician the same day for these routes.

10. Why does the calculator ask about body weight?

Some evidence links higher body weight with lower effectiveness. The note appears from 165 pounds upward in this tool. It prompts a conversation, not a refusal. A pharmacist may suggest an option unaffected by weight. Leaving it blank simply hides the note.

Practical Questions

11. What if I vomit after taking the pill?

Tell a pharmacist promptly. Vomiting soon after a dose can stop it absorbing properly. Guidance often considers another dose in that case. Only a professional can judge your case. Do not simply take extra pills on your own.

12. Does it protect me for the rest of the cycle?

No, it covers only the earlier act. Ovulation may only be delayed, not cancelled. Further unprotected sex in the same cycle can still lead to pregnancy. Use condoms until your next period. Consider regular contraception afterwards.

13. What if my period is late afterwards?

Take a pregnancy test if your period is over a week late. Also test if it seems unusually light. Emergency contraception can shift the next period slightly. A negative test with a missing period deserves a clinic visit.

14. Can I take it more than once?

It can be used again, including in the same cycle, if another risk occurs. Repeated use is less reliable than regular contraception, though. Side effects like cycle disruption also become likelier. A clinician can help you find a steadier method. Emergency pills are a backup, not a routine.

15. Does it protect against infections?

No, it offers no protection against infections at all. Only condoms reduce that risk. A sexual health check is wise after unprotected sex with a new partner. Many infections show no symptoms at first. Testing is quick and common, and nothing to feel embarrassed about.

CONCLUSION

Timing is the whole story with emergency contraception. The first day offers the strongest estimated protection, and every band after that is weaker. This calculator shows your band in seconds, plus the hours left in the main window. Use it to move faster, not to relax. Then get personal advice from a pharmacist or clinician today, while every option is still open. That one call is the step worth taking right now.