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Free health tool
Ovulation calculator Portugal
Enter the first day of your last period to see the six days you are most likely to conceive, your estimated ovulation day and when your next period is due.
- Counted back from your next period, so longer cycles are timed correctly
- The whole six-day fertile window, not a single day
- Runs in your browser — nothing is sent or stored
Your fertile window
The day bleeding started, not the day it stopped.
days
Days from the start of one period to the start of the next. Leave it at 28 if you are not sure.
15/01/2026
Estimated ovulation
Counted back 14 days from your next expected period, which is what keeps the timing right on cycles that are not 28 days long.
- Fertile window (6 days)
- 10/01 – 15/01
- Next period due
- 29/01/2026
- Test from
- 29/01/2026
An estimate from the dates you enter, not a diagnosis — and not a method of contraception. Ovulation moves from cycle to cycle, and pregnancy is possible on days outside the window shown.
01
Your cycle, day by day
A cycle is counted from the first day of bleeding. Ovulation is not pinned to day 14: it happens about 14 days before your NEXT period, so a 35-day cycle ovulates around day 21 and a 24-day cycle around day 10. That is why counting forward from your last period mis-times every cycle that is not 28 days.
The days below are one 28-day cycle. The calculator above shifts them to the cycle length you entered.
Day 1
- What is happening
- Bleeding starts — the cycle is counted from here
- Chance of conceiving
- Very low
Days 2 – 8
- What is happening
- An egg is maturing; the window has not opened yet
- Chance of conceiving
- Low
Days 9 – 13
- What is happening
- Fertile window: sperm can survive up to five days
- Chance of conceiving
- High
Day 14
- What is happening
- Ovulation — the egg is released
- Chance of conceiving
- Highest
Days 15 – 16
- What is happening
- The egg survives less than a day after release
- Chance of conceiving
- Falling fast
Day 28
- What is happening
- The next period is due — test from here if it does not arrive
- Chance of conceiving
- Very low
02
Signs you have actually ovulated
A calculator predicts; these confirm. Tracking one or two of them across a couple of cycles tells you whether your own ovulation matches the estimate — and that is worth knowing before you plan anything around it.
- Cervical mucus turns clear, stretchy and slippery, like raw egg white, in the days just before ovulation.
- Ovulation predictor kits detect the LH surge in urine, which comes 24 to 36 hours before the egg is released. Start testing a few days before the estimated date.
- Basal body temperature rises by around 0.3 °C after ovulation, so it confirms it afterwards rather than predicting it.
- Some people feel a one-sided ache mid-cycle, and some notice breast tenderness or a shift in libido.
- A cycle can pass without ovulation at all. That happens to most people occasionally and does not by itself mean anything is wrong.
03
What this calculator cannot do
It works from two things only: the date you enter and the assumption that your luteal phase is a standard 14 days. Both are reasonable, neither is guaranteed.
- It is not a method of contraception. Cycles move, sperm survive for days, and pregnancy is possible on days outside the window shown here.
- Irregular cycles, recently stopped hormonal contraception, breastfeeding, PCOS and thyroid conditions all weaken the prediction.
- Hormonal contraception suppresses ovulation, so there is nothing here to predict while you are using it.
- Stress, illness, travel and heavy training can all delay ovulation in a given cycle.
- It is a planning tool, not a fertility test: it says nothing about egg quality, sperm or the fallopian tubes.
04
When to talk to a doctor
- You have been trying to conceive for 12 months, or for 6 months if you are over 35.
- Your cycles are shorter than 21 days, longer than 35 days, or unpredictable from one month to the next.
- Your periods have stopped, or you are bleeding between them.
- You have painful periods, pain during sex, or a diagnosis of PCOS, endometriosis or a thyroid condition.
- You want preconception advice — folic acid, the medicines you already take, vaccinations and a blood pressure check all belong before a pregnancy rather than after it.
Where to go from here
An ovulation estimate is a timing guide, not a fertility assessment. These are the consultations our doctors run when you want someone to look at the whole picture.
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Ovulation calculator — FAQs
When am I most fertile?
On the day of ovulation and the two days before it. The window as a whole covers about six days: the five before ovulation plus the day itself. Sperm survive up to five days and the egg under one, which is why the window opens early and closes fast.
Does ovulation always happen on day 14?
No. Day 14 is only true of a textbook 28-day cycle. Ovulation sits roughly 14 days before your next period, so on a 32-day cycle it lands around day 18 and on a 24-day cycle around day 10. Counting 14 days forward from your last period is the commonest way to get the timing wrong.
How do I work out ovulation with irregular cycles?
Enter your usual cycle length and treat the result as a wide estimate rather than a date. If your cycles vary by more than a few days, ovulation predictor kits or tracking cervical mucus will tell you far more than any calendar calculation, and cycles that are consistently under 21 or over 35 days are worth a doctor's opinion.
Can I use an ovulation calculator as contraception?
No. It is not a contraceptive method and should never be used as one. Ovulation shifts between cycles, sperm can survive up to five days, and pregnancy is possible on days this calculator marks as outside the fertile window. If you are avoiding pregnancy, use a recognised method of contraception.
When can I take a pregnancy test after ovulation?
Most home tests are reliable from the day your period is due, which is about 14 days after ovulation — the "test from" date in the read-out. Testing earlier can give a negative result even when you are pregnant, because there is not yet enough hCG in urine to detect.
Does this ovulation calculator store my details?
No. The calculation runs entirely in your browser. Nothing you type is sent to our servers or saved.
Where do I get fertility advice in Portugal?
Start at your local health centre: the family doctor does the first assessment and blood tests for both partners and refers on to gynaecology or a reproductive medicine service when that is the next step. Our registered doctors can review irregular cycles and preconception checks by video in the meantime.
Where can I buy ovulation tests in Portugal?
In pharmacies and parapharmacies, without a prescription. They detect the LH surge in urine 24 to 36 hours before the egg is released, so start testing a few days before the date estimated above.
Trying to conceive?
Talk to a registered doctor by video about irregular cycles, preconception checks or the medicines you already take.