Period & pregnancy calculators
All 33 Period Tools calculators in one place — grouped so you can jump straight to what you need. Track your cycle, find your fertile window, count down a pregnancy, or settle a family debate with a baby-trait estimate. Everything here is free, runs privately in your browser, and needs no sign-up.
Period & cycle
Predict your period, measure your cycle, and make sense of a late or irregular month.
- Period CalculatorPredict your next few periods from your last start date and cycle length.
- Next Period CalculatorSee the single date your next period is most likely to arrive.
- Menstrual Cycle CalculatorMap your full cycle — period, fertile window, and ovulation — on one calendar.
- Cycle Length CalculatorWork out your average cycle length from a few recent start dates.
- Late Period CalculatorCount exactly how many days past due your period is.
- Missed Period CalculatorCheck whether a period is genuinely missed or just running late.
- Irregular Period CalculatorA wider, range-based estimate for cycles that vary month to month.
Ovulation & conception
Pinpoint your fertile days and the timing around conception and early testing.
- Fertile Window CalculatorFind the roughly six days each cycle when conception is most likely.
- Conception CalculatorEstimate when conception likely happened from your due date or last period.
- Implantation CalculatorEstimate the implantation window and when a test could first turn positive.
- Chances of Getting PregnantSee how the odds shift across the days of your cycle.
- hCG CalculatorTrack how your hCG level is doubling between two blood tests.
Pregnancy
From due dates to gestational age — the dates and milestones of pregnancy.
- Due Date CalculatorEstimate your due date from your last period or conception date.
- How Far Along Am I?Turn a date into weeks, days, and trimester at a glance.
- Pregnancy Test CalculatorFind the earliest day a test is likely to read accurately.
- Gestational Age CalculatorConvert dates into precise gestational age in weeks and days.
- Weeks to MonthsTranslate pregnancy weeks into months without the usual confusion.
- Reverse Due Date CalculatorWork backward from a due date to the likely conception window.
- IVF Due Date CalculatorDue dates for IVF transfers, adjusted for embryo day.
- Pregnancy Weight GainSee a healthy weight-gain range for your week and starting BMI.
Predictions & baby traits
Playful estimators for gender, eye and hair colour, height, and blood type. For curiosity, not certainty.
- Gender PredictorA just-for-fun prediction based on the Chinese gender chart.
- Baby Gender PredictorAnother playful boy-or-girl estimate to compare against.
- Baby Eye Color CalculatorEstimate the odds of brown, green, or blue eyes from both parents.
- Baby Hair Color CalculatorA playful guess at your baby's likely hair shade.
- Child Height CalculatorProject a child's adult height using the mid-parental method.
- Blood Type CalculatorWork out a child's possible ABO blood types — genuinely Mendelian.
- Punnett Square CalculatorBuild a Punnett square for any single-gene cross.
- Twin Probability CalculatorEstimate your odds of twins from the factors that actually matter.
- Baby Age CalculatorConvert a birth date into weeks and months old.
Quizzes & life stages
Quick self-checks for pregnancy signs, a first period, and the menopause transition.
Exploring inherited traits?
Several of the baby tools above touch on genetics. For the science behind them — what dominant and recessive really mean, and why earlobes and tongue rolling aren’t the simple one-gene traits textbooks claim — visit our human genetic traits hub.
Frequently asked questions
Are these calculators free to use?
Yes — every calculator on Period Tools is free, works in your browser, and needs no sign-up. Your dates stay on your device; we don't require an account to run any of the tools.
How accurate are period and ovulation calculators?
They're planning estimates, not guarantees. A calculator projects your most likely dates from the numbers you enter — your last period, your average cycle length — but real cycles shift with stress, travel, sleep, and health. Use the result as a helpful guide and expect some variation month to month.
Which calculator should I start with?
If you want to know when your next period is due, start with the Period Calculator. Trying to conceive? The Fertile Window and Ovulation tools are the place to begin. Already pregnant? Use the Due Date calculator, then How Far Along Am I to track the weeks.
Are the baby trait predictors real science?
Mostly they're for fun. Eye colour, hair colour, and height are shaped by many genes plus chance and environment, so any single estimate is a rough guess. The one genuinely rule-based tool is the Blood Type Calculator, because ABO blood groups really do follow clear inheritance patterns.
Can I use these instead of seeing a doctor?
No. Period Tools calculators are for planning and curiosity only. They don't diagnose anything and aren't a substitute for medical advice. If something about your cycle, fertility, or pregnancy worries you, talk to a healthcare professional.