Plan B Calculator

What This Calculator Does

The Plan B Calculator is a timing aid for emergency contraception. You enter the number of hours since unprotected intercourse, and it tells you whether you are inside the 72-hour window, inside the wider 120-hour window, or beyond both windows, along with how many hours remain in each window. The purpose is simple and urgent. Emergency contraception works best the sooner it is taken, and a clear statement of where you stand in time helps you act without delay instead of guessing from memory.

This tool does not diagnose, prescribe, or replace professional advice. It performs one calculation, which is comparing an entered number of hours against two fixed thresholds, 72 and 120. Everything else, including which product is appropriate, whether it is suitable for you, and what to do if the window has passed, belongs in a conversation with a clinician or pharmacist, ideally as soon as possible. If you are reading this because the event was recent, the most useful step is to contact a pharmacy or clinic now and use the calculator only to organise what you tell them.

The calculator is also deliberately limited in what it asks. It needs only the hours since intercourse, because that is the only input the window comparison requires. It does not ask for personal details, medical history, or identifying information, and nothing you enter is stored or sent anywhere. The result is computed in your browser the moment you press Calculate.

Why Timing Matters So Much

Emergency contraception works mainly by delaying ovulation, which means it must be taken before ovulation happens to have its intended effect. That is why effectiveness falls as hours pass. Levonorgestrel-based emergency contraception is generally described as effective for up to 72 hours, with some guidance extending its use to 120 hours at reduced effectiveness, while ulipristal acetate is generally described as effective for up to 120 hours. The exact product, dose, and eligibility depend on individual factors, which is why a pharmacist or clinician should confirm the choice.

The two thresholds in this calculator, 72 and 120 hours, therefore represent two different kinds of urgency. Inside 72 hours, you are within the window where levonorgestrel is usually discussed and where ulipristal is also an option. Between 72 and 120 hours, the first window has closed but the wider window may still be open, so acting immediately still matters. Beyond 120 hours, over-the-counter emergency contraception is generally no longer presented as an option, and a clinician can discuss alternatives such as a copper intrauterine device, which has a different time frame and requires a procedure.

Uncertainty about timing is common, and it is one of the reasons people delay. If you are unsure exactly how many hours have passed, use your best estimate and round toward the earlier side when you speak to a pharmacist, because an earlier estimate keeps more options open. If the event happened more than once, or if you are unsure which event matters, say so plainly when you seek advice, since that changes the calculation a clinician will make.

How to Use This Calculator

Work out the number of hours since unprotected intercourse as accurately as you can. If it happened yesterday evening and it is now the following afternoon, that is roughly 18 to 24 hours, depending on the exact times. Enter that number, press Calculate, and read the status line first. That line states whether you are within the 72-hour window, within the 120-hour window, or beyond both, and the lines below it show how many hours remain in each window.

Use the result to act, not to wait. If the result says hours remain, contact a pharmacy or clinic right away and tell them the number of hours and the result. If the result says the windows have passed, still contact a clinician promptly, because other options and advice, including pregnancy testing timelines and ongoing contraception, may still be relevant. Do not use the calculator repeatedly as a reason to postpone that call, since every hour that passes narrows the options further.

Worked Example

Suppose unprotected intercourse happened 36 hours ago. Entering 36 gives a status of within the 72-hour window, with 36 hours remaining in that window and 84 hours remaining in the 120-hour window. The practical message is clear. You are well inside both windows, but the clock is running, so contact a pharmacy or clinic now rather than waiting until the next day, when the remaining time will be shorter and the choice of product may narrow.

A second example shows the middle case. At 96 hours, the calculator reports within the 120-hour window, with zero hours remaining in the 72-hour window and 24 hours remaining in the 120-hour window. The 72-hour window has closed, but one full day remains in the wider window, so immediate action still matters. At 150 hours, the result is beyond the 120-hour window, with zero hours remaining in both, and the right step is prompt clinical advice about alternatives and next steps, including when a pregnancy test would be meaningful.

What the Calculator Cannot Do

The calculator cannot tell you which product to take, whether emergency contraception is safe for you, or whether it will work in your situation. Body weight, other medicines, vomiting shortly after taking a dose, breastfeeding, and medical history can all affect the advice a pharmacist or clinician gives, and none of those factors are inputs here. The tool also cannot confirm whether ovulation has already happened, which is the biological fact that ultimately determines effectiveness.

It also cannot help after the fact. If a pregnancy test later shows a positive result, or if you develop symptoms that worry you, seek clinical care directly rather than returning to a timing calculator. The same applies if the intercourse was not consensual. In that case, urgent medical care, support services, and, if you wish, reporting options are available, and a clinician or support service can help you through the immediate steps in confidence.

Common Mistakes

The most common mistake is waiting to see whether a period arrives before acting. Emergency contraception is time-sensitive by design, and waiting for a missed period removes the option entirely. A second mistake is assuming that one product covers any time frame. The 72-hour and 120-hour figures belong to different products and different guidance, so the product and the timing must be matched by a pharmacist or clinician, not assumed from a brand name remembered from advertising.

A third mistake is entering days instead of hours. Three days is 72 hours, and five days is 120 hours, so a small rounding error can move the result across a threshold. Enter hours as precisely as you can, and if you are near a boundary, say so when you seek advice. Finally, do not treat emergency contraception as a regular method. It is less reliable than ongoing contraception, and a clinician can help you choose a regular method that fits your life, which removes this kind of time pressure in future.

Getting Help Quickly

When time matters, the practical challenge is often not the calculation but the next step, which is reaching a pharmacist or clinician and explaining the situation clearly. Pharmacies are usually the fastest route, since many can supply levonorgestrel without a prescription and can advise on whether a prescription product or a clinic visit is more appropriate. Calling ahead saves a wasted trip if the pharmacy is closed or out of stock, and it lets you ask directly whether the pharmacist on duty can provide emergency contraception, since not every staff member in every setting can supply every product.

It helps to have a few facts ready before the call, because the pharmacist or clinician will ask them in order to give safe advice. Useful information includes the number of hours since intercourse, the date of the last menstrual period and whether cycles are usually regular, any medicines currently taken, any known allergies, and whether there is any chance of an existing pregnancy. Mentioning these facts plainly and without embarrassment makes the conversation faster and the advice more reliable, and pharmacists handle such conversations routinely and confidentially.

If cost is a barrier, say so, since options and prices vary, and clinics, family planning services, and some pharmacies offer reduced-cost or free provision depending on location and circumstances. If transport is a barrier, ask whether a nearby pharmacy delivers or whether a telephone consultation is possible. If language is a barrier, many services can arrange an interpreter, and bringing a trusted person to interpret is also an option. None of these obstacles should delay the call itself, since advice can often begin by phone while logistics are sorted.

After emergency contraception, ask about ongoing contraception at the same visit, since that conversation removes the risk of a repeat emergency. Options range from daily pills and patches to long-acting methods that need no daily attention, and the right choice depends on health, preferences, and plans. A clinician can also explain when a pregnancy test would be meaningful and what to do if a period is late, so that the period of uncertainty after the event is as short and as well understood as possible.

• Hours since unprotected intercourse, as accurately as you can estimate.
• Date of the last menstrual period and whether cycles are usually regular.
• Medicines currently taken, including over-the-counter products and supplements.
• Known allergies and any relevant medical history the pharmacist should know.
• Whether there is any chance of an existing pregnancy from an earlier event.

If you cannot reach a pharmacy today, do not simply wait until morning, especially if the 72-hour or 120-hour boundary falls overnight. Urgent care centres, sexual health clinics, and family planning services often have longer hours than high street pharmacies, and many offer telephone advice that can confirm the next step even when the building is closed. Some areas also offer online consultations that can arrange supply or a prescription quickly, and a hospital emergency department can advise in situations where no other route is available. The key point is that the clock does not pause for opening hours, so the effort should go into finding any open route now rather than into finding the most convenient route tomorrow. If the barrier is privacy, remember that pharmacists and clinicians handle these requests every day, that consultations are confidential, and that you can ask to speak privately or by phone. If the barrier is cost, say so at the start of the conversation, since free or reduced-cost provision exists in many areas and the pharmacist can direct you to it. Every hour spent searching is an hour closer to a closed window, so make the first call to the most available service and let them redirect you if needed.

Frequently Asked Questions

What is emergency contraception?

Emergency contraception is a method used after unprotected intercourse to reduce the chance of pregnancy, mainly by delaying ovulation. It includes levonorgestrel and ulipristal tablets and the copper intrauterine device, each with its own time frame and eligibility rules.

How does this calculator work?

It compares the hours you enter against two thresholds, 72 and 120 hours, and reports whether you are inside the first window, inside the wider window, or beyond both, plus how many hours remain in each window.

Is levonorgestrel effective after 72 hours?

Levonorgestrel is generally described as effective for up to 72 hours, with some guidance extending use to 120 hours at reduced effectiveness. A pharmacist or clinician should confirm what applies to you, since guidance and products vary by location.

What about ulipristal acetate?

Ulipristal acetate is generally described as effective for up to 120 hours after unprotected intercourse. It usually requires a prescription or pharmacist supply depending on local rules, so ask a pharmacist or clinician promptly.

What if more than 120 hours have passed?

Over-the-counter emergency contraception is generally no longer presented as an option after 120 hours. A clinician can still discuss alternatives, including a copper intrauterine device, and advise on pregnancy testing timelines and ongoing contraception.

Does body weight affect emergency contraception?

Body weight can affect the advice given for some emergency contraception, which is one reason a pharmacist or clinician should be consulted. Do not adjust a dose yourself, and mention your weight honestly when seeking advice.

What if I vomit after taking it?

Vomiting shortly after a dose can affect absorption, and the correct step depends on timing and the product. Contact a pharmacist or clinician promptly for advice rather than guessing whether to repeat the dose.

Can I take emergency contraception more than once?

It can be used more than once, but it is not intended as a regular method because it is less reliable than ongoing contraception. A clinician can help you choose a regular method that avoids repeated emergencies.

Does emergency contraception cause an abortion?

No. Emergency contraception works mainly by delaying ovulation and does not end an established pregnancy. If a pregnancy is already established, it will not be affected, and clinical advice should be sought.

When should I take a pregnancy test?

A pregnancy test is usually meaningful from around the time of an expected period, and sometimes a few weeks after the event. A clinician or pharmacist can advise on timing for your situation, especially if your cycle is irregular.

Is emergency contraception available without prescription?

Availability depends on location and product. Levonorgestrel is available without prescription in many places, while ulipristal often requires pharmacist or clinician supply. A local pharmacy can confirm the current rules quickly.

What if the intercourse was not consensual?

Seek urgent medical care and support as soon as you feel able. Clinicians and support services can provide emergency contraception, testing, and confidential advice, and can discuss reporting options only if and when you wish.

Can teenagers access emergency contraception?

Rules vary by location, and many pharmacies can supply emergency contraception to teenagers. A pharmacist can explain local rules confidentially, and acting promptly matters more than worrying about embarrassment.

Does this calculator store my information?

No. The calculation happens in your browser when you press Calculate, and nothing is sent or stored. You can close the page immediately after seeing the result.

What should I do right now?

If the event was recent, contact a pharmacy or clinic immediately, tell them the number of hours, and follow their advice. Every hour matters, so make the call before doing anything else.