Cycle phase calculator / Cycle day 13
Cycle day 13: what phase am I in?
On a 28-day cycle, day 13 is usually the ovulatory phase. Across normal cycle lengths it can be follicular, ovulatory or luteal, because ovulation happens about 14 days before your next period, not on a fixed day.
Day 13 opens the ovulatory window on a 28-day cycle. If you track ovulation with LH strips, the surge often shows up around now.
Day 13 across different cycle lengths
| Cycle length | Day 13 is | Ovulation around |
|---|---|---|
| 24 days | Luteal phase | Day 10 |
| 26 days | Ovulatory phase | Day 12 |
| 28 days | Ovulatory phase | Day 14 |
| 30 days | Follicular phase | Day 16 |
| 32 days | Follicular phase | Day 18 |
| 35 days | Follicular phase | Day 21 |
Assumes a 5-day period and a 14-day luteal phase, the same model the Phaes app uses. Your own cycle can vary by a few days from month to month.
What is happening in your body
Estrogen peaks and a surge of luteinizing hormone (LH) triggers ovulation, the release of an egg. Testosterone rises slightly too. This window lasts only a few days.
Many women feel strong and social. Some notice mid-cycle twinges on one side, which is common.
How to train on day 13
Running
Quality work still suits: this is a fine day for a hard session if your plan has one. Warm up properly before fast running.
Strength
Your peak strength window. Phaes pushes the hardest set of the cycle around ovulation.
Fuel
Eat enough to match the training: under-fueling around hard sessions shows up later in the cycle.
Treat this as a starting point. A meta-analysis of 78 studies found that cycle phase has at most a trivial effect on performance on average, with big differences between women (McNulty et al., 2020). How you slept and how you feel today should win.
Not sure which day you are on?
Enter the first day of your last period and your usual cycle length.
Find my phase todayIf your cycles are changing
In perimenopause cycles get shorter, then longer and less predictable, and ovulation does not happen every month, so a day number stops telling you much about your hormones. The training answer changes too: short sprints over long slow miles, lifting heavy, easy days that are genuinely easy, one full rest day a week and a reset week every fourth week. Take the perimenopause quiz if you are not sure where you are.
Let your plan follow your real cycle
Phaes anchors to the periods you log, projects your phases from your own cycle, and moves your hard runs, strength and rest days around them and a 30-second daily check-in.
Get started with PhaesFree to download. Your first week is on us.
Questions women ask about day 13
What phase is day 13 of my cycle?
On a 28-day cycle, day 13 is usually the ovulatory phase. Across normal cycle lengths it can be follicular, ovulatory or luteal, because ovulation happens about 14 days before your next period, not on a fixed day.
Should I work out on day 13 of my cycle?
Yes, if you feel up to it. Quality work still suits: this is a fine day for a hard session if your plan has one. Warm up properly before fast running.
How should I lift weights on cycle day 13?
Your peak strength window. Phaes pushes the hardest set of the cycle around ovulation.