Period Calculator
HealthPredict your next period date, cycle day, and upcoming periods for the next 3 months. Track your menstrual cycle with ease.
8th June 2026
Average Cycle Length
days
20 days45 days
Period Duration
days
2 days10 days
Next Period
15th June 2026
Starting today · ends 15th June 2026
Days Away
0
Cycle Day
Day 1
Period Duration
5 days
Cycles Tracked
0
Day 1Day 1Day 28
Upcoming Periods
15th June 2026
ends 19th June 2026
13th July 2026
ends 17th July 2026
10th August 2026
ends 14th August 2026
What is a Period?
A Period Calculator predicts the date of your next menstrual period, tells you which day of your current cycle you are on, and helps you plan for upcoming periods over the next several months. It works by applying your average cycle length to your last period date to project forward.
Menstrual cycle tracking is the foundation of reproductive health awareness. Knowing where you are in your cycle helps you:
- Plan around an upcoming period for travel, events, or examinations
- Identify fertile windows (use the Ovulation Calculator for this)
- Spot irregularities that may indicate a health concern
- Track PMS patterns and understand symptom timing relative to your cycle
The calculator outputs the days until your next period (as a number to add to today's date), your current cycle day, and days until the next period ends — giving you the full picture of your cycle position in real time.
How to use this Period calculator
- Enter the first day of your last period in the date field — the day bleeding started, even if light.
- Enter your average cycle length in days. If unsure, count the days between the start of your last two periods.
- Enter your typical period duration in days (how many days bleeding usually lasts).
- Days until next period is the primary result — add this to today's date to find the calendar date.
- Current day in cycle tells you where you are right now in your cycle.
- Period ends shows how many days after today the next period will end.
- Use this alongside the Ovulation Calculator to track both your period and fertile window together.
Formula & Methodology
Days since LMP = Today − Last period date Cycles elapsed = Floor(days since LMP ÷ cycle length) Current day in cycle = (Days since LMP mod cycle length) + 1 Next period start = LMP + (cycles elapsed + 1) × cycle length Days until next period = Next period start − Today Period end = Days until next period + period duration − 1Worked example — Last period 15 May, cycle 30 days, duration 5 days, today is 10 June:Days since LMP = 26 days Cycles elapsed = Floor(26 ÷ 30) = 0 full cycles Current cycle day = (26 mod 30) + 1 = Day 27 Next period start = 15 May + 30 days = 14 June Days until next period = 14 June − 10 June = 4 days Period ends = 4 + 5 − 1 = 8 days away (19 June)Normal menstrual cycle reference: | Parameter | Normal range | |---|---| | Cycle length | 21–35 days | | Period duration | 3–7 days | | Blood loss | 5–80 mL per cycle | | Follicular phase | 7–21 days (variable) | | Luteal phase | 10–16 days (relatively fixed) |
Frequently Asked Questions
What is a menstrual cycle and how long is it?
A menstrual cycle is the monthly hormonal cycle that prepares the female body for potential pregnancy. It is counted from the first day of one period to the first day of the next. The average cycle length is 28 days, but normal cycles range from 21 to 35 days. Period duration (the bleeding phase) typically lasts 3–7 days. Both cycle length and period duration can vary month to month, especially during adolescence, perimenopause, or periods of stress.
How does the Period Calculator predict the next period?
The calculator uses your last period start date and your average cycle length to predict the next period: Next period start = Last period date + Cycle length. If you entered a 30-day cycle that started on 1 May, the next period is predicted for 31 May. The 'current day in cycle' counts how many days have passed in your current cycle since the last period started. The result is a statistical prediction — actual timing may vary by a few days.
What does 'current day in cycle' mean?
The current cycle day tells you where you are in your menstrual cycle right now. Day 1 is the first day of your period. Days 1–5 (approximately) are the menstrual phase (bleeding). Days 6–13 are the follicular phase (eggs developing). Day 14 (in a 28-day cycle) is roughly ovulation. Days 15–28 are the luteal phase (post-ovulation). Knowing your cycle day helps you understand current symptoms, energy patterns, and fertility status.
Is it normal for periods to be irregular?
Some variation is normal — most women's cycles vary by 1–5 days month to month. Cycles that vary by more than 7 days are considered irregular. Common causes of irregular periods in India include PCOS (polycystic ovary syndrome), thyroid disorders, stress, extreme weight changes, high physical training loads, and breastfeeding. Irregular periods should be discussed with a gynaecologist, especially if trying to conceive or if accompanied by heavy bleeding, severe pain, or spotting between periods.
Can I use this calculator if I have irregular cycles?
You can use this calculator with your average cycle length (calculated over 3–6 months), but the prediction accuracy will be lower for irregular cycles. For women whose cycles vary by more than 7 days, the next period date may be off by a week or more. Period tracking apps that build an adaptive model from your history (like Clue or Flo) give better predictions for irregular cycles. If irregularity is significant, a gynaecologist can investigate underlying conditions.
How do I calculate my average cycle length?
Count the number of days from the first day of one period to the first day of the next period — that is one cycle. Track 3–6 cycles and calculate the average: add all cycle lengths and divide by the number of cycles. For example: 28 + 30 + 27 + 29 = 114 ÷ 4 = 28.5 days, round to 29 days. The more cycles you track, the more accurate your average. A period tracking app can do this automatically.
What are the phases of the menstrual cycle?
The four phases are: Menstrual phase (days 1–5): shedding of the uterine lining, bleeding occurs. Follicular phase (days 1–13): overlaps with menstrual phase; follicles develop in the ovaries, oestrogen rises. Ovulation (around day 14 in a 28-day cycle): egg is released; peak fertility. Luteal phase (days 15–28): progesterone rises to prepare the uterus for implantation; if no pregnancy occurs, progesterone drops and the next period begins. PMS symptoms (mood changes, bloating, cramps) typically occur in the late luteal phase (days 22–28).
How do I use the Period Calculator?
Enter the first day of your most recent period in the date field. Enter your average cycle length in days (default 28). Enter how many days your period typically lasts (default 5). The result shows days until your next period starts, your current day in the cycle, and when the next period will end. Add the 'days until next period' to today's date to find the exact calendar date of your next expected period.
Can I use this to avoid pregnancy (natural family planning)?
Calendar-based methods alone are not a reliable contraceptive. The rhythm method (avoiding intercourse around estimated ovulation) has a typical-use failure rate of 24% per year — meaning about 1 in 4 women using it will become pregnant annually. For natural family planning, the Symptothermal Method (combining calendar tracking with BBT temperature charts and cervical mucus observation) is more effective but still less reliable than hormonal methods. Consult a gynaecologist for contraception advice appropriate to your situation.
What is considered a late period?
A period is generally considered late if it has not started within 5 days of the expected date. Most pregnancy tests are reliable 1–2 days after a missed period. Common non-pregnancy causes of a late period include stress, illness, significant exercise changes, weight changes, travel across time zones, hormonal fluctuations, and perimenopause. In India, thyroid disorders and PCOS are two very common medical causes — both detectable via simple blood tests that a gynaecologist can order.
What is PMS and when does it occur?
Premenstrual syndrome (PMS) refers to physical and emotional symptoms that occur in the 1–2 weeks before a period (the luteal phase). Common symptoms include mood changes, irritability, bloating, breast tenderness, headaches, and fatigue. Symptoms typically resolve within 2–3 days of the period starting. Severe PMS with significant mood disruption is called PMDD (Premenstrual Dysphoric Disorder). Knowing your cycle day from this calculator helps identify whether symptoms are cycle-related versus other causes.