Free Women's Health Calculators
Quick, accurate calculators for due date, ovulation, your next period, pregnancy week, and cycle length. No sign-up, no data stored, no apps to install.
Due Date Calculator
Enter the first day of your last period to find out when your baby is due, what trimester you're in, and how big your baby is right now.
Calculate due dateOvulation Calculator
Estimate when you're ovulating and identify your fertile window — the 6 days each cycle when conception is most likely.
Find your fertile windowPeriod Calculator
Predict when your next period will start and see the next 6 months of expected periods at a glance.
Predict next periodPregnancy Week Calculator
Find out exactly how far along you are, what's happening with baby this week, and what milestones are coming up.
See your weekCycle Length Calculator
Enter your last 3–12 period dates to calculate your average cycle length, see how regular your cycles are, and spot patterns.
Check cycle regularityBuilt by women, backed by the math your doctor uses
Every calculator on this page uses the same established formulas clinicians rely on — and runs entirely in your browser, so your dates stay on your device.
Instant results
Pick a date, get your answer. No loading screens, no waiting.
Private by design
Calculations happen in your browser. We never store the dates you enter.
Clinician-aligned math
Naegele's Rule, the cycle-length-minus-14 method, and weighted averages — the same formulas your doctor uses.
How to choose the right calculator
Each tool answers a different question. Most people use two or three of these together at different points in their cycle or life stage.
If you're trying to conceive
Start with the ovulation calculator to find your fertile window, then use the cycle length calculator if your cycles aren't textbook 28 days — irregular cycle length is the #1 reason ovulation predictions go wrong. Once you get a positive test, switch to the due date calculator.
If you're already pregnant
The due date calculator gives you your estimated delivery date. The pregnancy week calculator tells you exactly how far along you are right now, what's happening with baby this week, and what milestones are coming.
If you just want to know when your next period is coming
The period calculator predicts your next period from your last period date and average cycle length. If you're not sure how regular your cycles are, run the cycle length calculator first.
If your cycles feel off
Start with the cycle length calculator. Plug in your last 3-12 period start dates and you'll see whether your cycles are regular, somewhat irregular, or irregular — and what that pattern can mean (PCOS, perimenopause, post-pill, stress, thyroid). Read the period tracking guide for the full beginner walkthrough.
What calculators can't tell you
Every tool on this page runs the same math your doctor uses — Naegele's Rule, cycle-length-minus-14, weighted averages. That math is genuinely useful for a one-time answer. It's also working with very limited information about you.
Calculators don't know if you're actually ovulating
The ovulation calculator assumes you ovulate around 14 days before your next period. That's true for most people most of the time. It's not true for cycles where ovulation didn't happen (anovulation, which is common in PCOS, post-pill, postpartum, and perimenopause), and it can be off by days even in regular cycles. Tracking BBT, cervical fluid, or LH tests over a few months tells you what calendar math can't.
Calculators don't know your cycle history
A calculator can only do math on the numbers you give it today. A tracking app sees the last 3, 6, 12 months — which is what your doctor needs to spot patterns and what your provider compares against when something changes.
Calculators don't know your symptoms
"When is my next period?" is a useful question. "Why do I get migraines two days before my period?" or "Is this breast tenderness normal for week 8?" are the questions that actually shape care. Calculators can't answer those. Tracking can.
Bottom line: Calculators are the right tool for a one-time answer. If you're trying to conceive, managing PCOS or perimenopause, navigating pregnancy, or want a real conversation with your doctor next visit — that's where tracking compounds.
Cycles aren't textbook. Yours shouldn't be either.
Calculators give you one answer based on averages. Go Go Gaia learns from your actual cycle history — irregular, regular, post-pill, post-baby — and sharpens its predictions every time you log a period, an ovulation sign, or a symptom. Built for real bodies, including PCOS, perimenopause, and everything in between.
Get Go Go GaiaFrequently Asked Questions
Educational content, not medical advice. These calculators use established formulas (Naegele's Rule for due dates, cycle-length-minus-14 for ovulation, weighted averages for period predictions) to give you an estimate, not a diagnosis or treatment recommendation. They are not intended for contraception. For pregnancy care, fertility planning, contraception, or any symptoms or cycle patterns that concern you, please consult your healthcare provider. Go Go Gaia is a tracking tool, not a substitute for professional medical care.