Pick your method and the first day of your last period, and this works out whether you are protected from pregnancy straight away or on a later date. The rules follow current NHS guidance: starting fresh, not switching from another hormonal method, and not after birth, a miscarriage or an abortion — those cases have their own rules, so follow your leaflet or ask a doctor, nurse or pharmacist.
When does birth control start working?
Method & cycle day → protected from
Your method and when you started
Nothing you type here leaves your browser.
How this is worked out
Your cycle day is the number of days from the first day of your last period to the day you start the method, counting the first day of your period as day 1. If you start on day 1 you are on day 1, start the next day you are on day 2, and so on.
Each method has a window at the start of the cycle where you are protected straight away. Outside that window you still need to use extra contraception (for example condoms) for a few days. The windows and the number of extra days are what the NHS pages for each method say — this calculator is doing arithmetic, not changing them.
The rule for each method
| Method | Protected straight away on | Otherwise, extra contraception for |
|---|---|---|
| Combined pill (most brands) | Cycle days 1–5 | 7 days |
| Zoely | Day 1 only | 7 days |
| Qlaira | Day 1 only | 9 days |
| Traditional progestogen-only pill | Cycle days 1–5 | 2 days |
| Desogestrel pill | Cycle days 1–5 | 2 days |
| Drospirenone-only pill | Day 1 only | 7 days |
| Vaginal ring | Cycle days 1–5 | 7 days |
| Contraceptive injection | Cycle days 1–5 | 7 days |
Sources: NHS pages on the combined pill, the progestogen-only pill, the vaginal ring and the contraceptive injection.
When this tool does not apply
This is for someone starting a method fresh. Switching from another hormonal method, starting after giving birth, after a miscarriage or after an abortion all have their own rules, and some of them do give protection straight away whatever the cycle day. Follow the leaflet that comes with your method, and if anything is unclear your pharmacist can usually confirm it in a minute.
This is a reminder-planning tool, not medical advice, and it does not promise pregnancy prevention — no method does. If you miss pills, start late, vomit within hours of a pill or have severe diarrhoea, check the leaflet or NHS 111 for what to do.
Setting the reminders
Once you know the date you are protected from, the next job is remembering the pill at the same time every day. Doz keeps the daily reminder and the pack dates in one place, free for one or two medications and without an account.
Common questions
When does the combined pill start working?
Straight away if you start on days 1 to 5 of your cycle (day 1 is the first day of your period). On any other day of the cycle you are protected after 7 days of pills, and should use extra contraception such as condoms in that first week. Zoely and Qlaira are exceptions — they only give immediate protection when started on day 1, and Qlaira needs 9 days of pills otherwise.
When does the progestogen-only pill start working?
The traditional and desogestrel progestogen-only pills are protective straight away if you start on days 1 to 5 of your cycle, and after 2 days of pills if you start on any other day. The drospirenone-only pill only gives immediate protection when started on day 1, and otherwise needs 7 days before you are protected.
When does the contraceptive injection start working?
If you have the injection on days 1 to 5 of your cycle you are protected straight away. On any other day you are protected after 7 days, and should use extra contraception until then.
When does the vaginal ring start working?
Protected straight away if you insert it on days 1 to 5 of your cycle, and after 7 days of use if you insert it on any other day.
What is cycle day 1?
Day 1 is the first day of your period — the first day you bleed, not spotting the day before. If your period started on Monday the 5th and you start the method on Friday the 9th, you are on cycle day 5.
I might already be pregnant before I start — what should I do?
NHS advises a pregnancy test 3 weeks after the last time you had sex without contraception. Starting a method does not undo an existing pregnancy, so check the test result before relying on it.
One thing this cannot do
This is an arithmetic tool, not medical advice. It works out numbers from what you type in — it does not know your medication, your prescription, or what you should do if something goes wrong. Anything about changing a dose, spacing doses differently, or handling a missed dose is a question for your doctor or pharmacist.