Day 15 of the menstrual cycle
In short: what happens on day 15?
Day 15 of the menstrual cycle is the first day after ovulation and the start of the luteal phase. The ruptured follicle turns into the corpus luteum and begins producing progesterone. Because the egg can survive for up to 24 hours, pregnancy is still possible early in the day, then the chance drops quickly.
Day 15 of the menstrual cycle – animated explainer
Day 15: cycle dial, uterus and ovaries, hormone levels (illustrative animation).
What the animation shows
- FSH
- Follicle-stimulating hormone: starts the growth of follicles in the ovary
- LH
- Luteinising hormone: its sudden surge triggers ovulation
- E2
- Oestrogen (oestradiol): thickens the lining of the uterus
- P4
- Progesterone: prepares the uterus for a possible pregnancy
- BBT
- Thermometer and dots below: basal body temperature
- RING
- Coloured ring: the 28-day cycle and its phases; the green arc marks the fertile days
- MM
- The measurement in the uterus shows lining thickness; in the ovary it shows follicle or corpus luteum size
Phase
Luteal phase
Chance of pregnancy
Moderate
Uterine lining
11.5 mm
Corpus luteum
18 mm
FSH
36
LH
48
Oestrogen
55
Basal body temperature
36.55°C
What is happening in your body today?
If fertilisation happens, it takes place in the fallopian tube around this time. Under the influence of progesterone, the uterine lining begins to change into a secretory lining.
Hormones
Progesterone rises; LH and oestrogen fall. Basal body temperature rises by 0.3–0.5 °C.
How you might feel
Energy may dip slightly; discharge becomes thicker and less abundant.
Chance of pregnancy
The chance of pregnancy is moderate and falls quickly during the day.
Tips for today
- A rise in basal body temperature shows that ovulation has happened
- If you are trying to conceive, keep taking the vitamins your doctor recommended
- Make good-quality sleep a priority
When to see a doctor
See your doctor if you have severe pelvic pain, a fever or unusual bleeding.
Menstrual cycle day by day: table
| Day | What happens | Fertile window |
|---|---|---|
| Day 1 | First Day of Your Period | — |
| Day 2 | Heaviest Bleeding Day | — |
| Day 3 | FSH Rises, Follicles Grow | — |
| Day 4 | Bleeding Eases, Oestrogen Rises | — |
| Day 5 | Last Day of Your Period | — |
| Day 6 | Follicular Phase Begins | — |
| Day 7 | Dominant Follicle Is Selected | — |
| Day 8 | Oestrogen Rises, Fertile Window Nears | Low |
| Day 9 | Fertile Window Begins | Moderate |
| Day 10 | Fertile Window, Higher Pregnancy Odds | Moderate |
| Day 11 | 3 Days Before Ovulation | High |
| Day 12 | Oestrogen Nears Its Peak | High |
| Day 13 | LH Surge: Ovulation Is Near | Highest |
| Day 14 | Ovulation Day | Highest |
| Day 15 | Luteal Phase Begins | Moderate |
| Day 16 | Progesterone Rises | Low |
| Day 17 | Luteal Phase and Increased Appetite | — |
| Day 18 | Breast Tenderness May Start | — |
| Day 19 | Implantation Window Opens | — |
| Day 20 | Implantation Bleeding Possible | — |
| Day 21 | Progesterone Peak (Day 21 Test) | — |
| Day 22 | Mid-Luteal Phase | — |
| Day 23 | PMS Symptoms May Start | — |
| Day 24 | Hormones Start to Fall | — |
| Day 25 | Late Luteal Phase and PMS | — |
| Day 26 | Progesterone Drop and Cramps | — |
| Day 27 | 1 Day Before Your Period | — |
| Day 28 | Last Day of Your Cycle | — |
Frequently asked questions
Can you get pregnant the day after ovulation?
Because the egg survives for 12–24 hours, pregnancy is possible in the hours right after ovulation; after 24 hours the chance is very low.
What is the corpus luteum?
It is a temporary structure that forms from the follicle after the egg is released and produces progesterone. If there is no pregnancy, it shrinks within about 10–14 days.
Why does basal body temperature rise after ovulation?
Rising progesterone after ovulation increases body temperature by 0.3–0.5 °C, and this rise lasts until your period.
Gynaecology check-ups and follow-up at SoftCare Clinic
Book an appointment with our specialist doctors for irregular periods, painful periods or pregnancy planning.
The information on this page is general guidance based on a typical 28-day cycle and does not replace a medical examination. It should not be used as a method of contraception.
Medical content editor: Op. Dr. Şükrü Sanus