What cycle phase am I in today?
Enter the first day of your last period and your average cycle length to find out exactly what day of your cycle you're on, which of the four phases you're in right now, and when the next phase begins.
Why these dates? The math we use
Same counting method as the MoodSwings app (algorithm v2.0.0): your next period is your last start plus your cycle length; ovulation is estimated by counting 15 days back from that next period, because the luteal phase is more consistent than the first half of the cycle. The fertile window shown is the deliberately-wide estimate we give a brand-new user (6 days before ovulation to 4 after) — with only one cycle to go on, honesty beats false precision. As the app learns your real pattern it narrows the window. For cycles under 20 days a meaningful ovulation estimate isn't possible from dates alone, so we don't show one.
Know your phase without the math
MoodSwings shows your phase every day — plus how your moods, energy and symptoms map to it over time.
Estimates for education, not medical advice — and not a contraception method. Cycles shift with stress, sleep, travel and health.
The four phases of your menstrual cycle
Your cycle isn't one long stretch of "before" and "during" your period — it moves through four phases, each with its own hormonal weather. Knowing which one you're in explains a lot: why your energy is high one week and flat the next, why your skin changes, why PMS shows up on schedule. Here's the quick map.
Menstrual phase (roughly days 1–5) — your period. Hormones are at their lowest, energy often dips, and rest tends to feel good. Follicular phase (after your period to just before ovulation) — estrogen climbs, energy and mood usually lift, and it's a natural time for harder workouts and new plans. Ovulation phase (mid-cycle, ~14 days before your next period) — your fertile window; libido and energy often peak. Luteal phase (after ovulation to your next period) — progesterone rises then falls, which is when PMS, cravings, bloating and mood swings tend to appear.
How this calculator finds your phase
The one fixed point in most cycles is that ovulation happens about 14 days before the next period, no matter how long the whole cycle is. So the calculator takes your last period start, adds your cycle length to estimate the next period, counts back 14 days for ovulation, and lays the four phases around it. Your period length sets where the menstrual phase ends. It's an estimate — real cycles drift by a few days — but it's the same model your body roughly follows, and it's what MoodSwings refines automatically as you track.
Questions people ask
What cycle day am I on?
Your cycle day is the number of days since the first day of your last period, counting that first day as day 1. If your period started 10 days ago, you are on cycle day 11 today. Enter your last period start date above and the calculator counts it for you and tells you which phase that day falls in.
What are the four phases of the menstrual cycle?
The menstrual phase (your period, roughly days 1–5), the follicular phase (after your period until ovulation, when energy usually rises), the ovulation phase (the fertile window mid-cycle, around 14 days before your next period), and the luteal phase (after ovulation until your next period, when PMS can appear). Their exact lengths shift with your cycle length.
How do I know which phase I am in today?
You need two things: the first day of your last period and your average cycle length. From those, ovulation is estimated about 14 days before your next expected period, and the four phases fall into place around it. This tool does that maths and shows you today’s phase plus the dates each phase starts.
Why does my cycle phase matter?
Each phase comes with its own hormonal shifts — energy, mood, skin, appetite, sleep and PMS all move with them. Knowing your phase helps you plan workouts, expect mood changes, and understand symptoms instead of being surprised by them. MoodSwings tracks your phase automatically every day and tells you what to expect. Free to try on iPhone.