Pregnancy & Women's HealthMenstrual Cycle Forecasting Algorithm

Period Calculator

Forecasts future period start dates, cycle phases (follicular, ovulatory, luteal), and predicted premenstrual symptom (PMS) days.

Pregnancy & Women's Health• Menstrual Cycle Forecasting Algorithm

Predict your next menstrual period dates, cycle lengths, and PMS windows.

First Day of Last Period (LMP)

Average Cycle Length (Days)20 – 45 days

days

Period Bleeding Duration (Days)2 – 10 days

days

Day 71 of CycleLuteal Phase

Cycle 1 Period:Sep 16, 2026 – Sep 20, 2026

Fertile: Sep 25, 2026 – Oct 1, 2026PMS: Sep 11, 2026 – Sep 15, 2026

Cycle 2 Period:Oct 14, 2026 – Oct 18, 2026

Fertile: Oct 23, 2026 – Oct 29, 2026PMS: Oct 9, 2026 – Oct 13, 2026

Cycle 3 Period:Nov 11, 2026 – Nov 15, 2026

Fertile: Nov 20, 2026 – Nov 26, 2026PMS: Nov 6, 2026 – Nov 10, 2026

Evidence-based estimations. Consult a physician for personalized guidance.

Clinical Formula & Calculation Standard

Official clinical definitions and validated mathematical models

Next Period = LMP + Cycle Length | Follicular -> Ovulatory -> Luteal Phases

Models cycle variability, premenstrual symptom (PMS) intervals, and upcoming menses across consecutive cycles.

Standard menstrual cycle length ranges between 21 and 35 days (average 28 days).
Menstrual bleeding typically lasts between 2 and 7 days.

Track pregnancy progress, current week, trimester, and key developmental milestones.

Calculate estimated date of delivery (EDD) based on LMP, conception, or IVF date.

Track healthy weekly weight gain targets during pregnancy based on pre-pregnancy BMI.