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Health & Wellness Calculator Guides
Plain-language guides that explain the math behind our most-used calculators — sleep cycles, BMI, menstrual phases, and pregnancy due dates — with examples and direct links to the tools.
Sleep guides
How to Calculate Sleep Cycles
Learn how to calculate sleep cycles, why many people use 90-minute sleep cycles, and how a sleep cycle calculator can help estimate bedtime or wake-up time.
What Time Should I Go to Sleep?
Find out what time you should go to sleep based on your wake-up time, sleep cycles, and recommended sleep duration.
Is 90 Minutes Really a Full Sleep Cycle?
Learn whether 90 minutes is really a full sleep cycle and why sleep-cycle calculators use 90-minute estimates.
Best Wake-Up Time Based on Sleep Cycles
Learn how to choose the best wake-up time based on sleep cycles and how a sleep cycle calculator can estimate more refreshing wake times.
Sleep Cycle Calculator vs Sleep Timer
Compare a sleep cycle calculator and a sleep timer to understand which tool helps with bedtime, wake-up time, and sleep planning.
BMI guides
How to Calculate BMI Using Imperial Units
Learn how to calculate BMI using imperial units with pounds and inches, plus examples and BMI category explanations.
BMI Formula for Pounds and Inches
Use the BMI formula for pounds and inches to calculate body mass index with an easy step-by-step example.
BMI Chart for Women
Use a BMI chart for women to understand adult BMI categories, healthy BMI range, and important limitations.
BMI Metric vs Imperial Formula
Compare the metric and imperial BMI formulas and learn how to calculate BMI using kilograms, meters, pounds, and inches.
What Is a Healthy BMI?
Learn what a healthy BMI is, adult BMI categories, and why BMI should be used as a screening tool rather than a full health diagnosis.
Menstrual Cycle guides
How to Calculate Menstrual Cycle Length
Learn how to calculate menstrual cycle length by counting from the first day of one period to the first day of the next period.
What Is the Average Menstrual Cycle Length?
Learn the average menstrual cycle length, what counts as cycle length, and why normal cycle timing can vary.
Period Length vs Cycle Length
Learn the difference between period length and cycle length, and why both matter for menstrual tracking.
Follicular Phase vs Luteal Phase
Compare the follicular phase and luteal phase, including timing, hormones, ovulation, symptoms, and cycle tracking.
What Menstrual Phase Am I In?
Learn how to estimate your menstrual phase based on your period start date, cycle length, ovulation timing, and symptoms.
How to Calculate Your Menstrual Cycle
Learn how to calculate your menstrual cycle, count cycle days, understand average cycle length, and track your period more accurately.
How to Calculate Cycle Length
Learn how to calculate cycle length, count the days in your menstrual cycle, and find your average cycle length.
What Is the Average Menstrual Cycle Length?
Learn the average menstrual cycle length, how to calculate your own cycle average, and what irregular cycle lengths may mean.
When Is the Luteal Phase?
Learn when the luteal phase happens, how to calculate it, how long it lasts, and why it matters for your menstrual cycle.
Pregnancy guides
How to Calculate Pregnancy Due Date
Learn how to calculate a pregnancy due date using last menstrual period, ovulation date, conception date, or ultrasound dating.
Due Date Calculator for 32-Day Cycle
Learn how a due date calculator works for a 32-day cycle and why ovulation may happen later than in a 28-day cycle.
Last Period Due Date Calculator Explained
Learn how a last period due date calculator works and why the first day of your last menstrual period is used.
Pregnancy Due Date by Ovulation Date
Learn how to calculate pregnancy due date by ovulation date and why it may be useful for people who track ovulation.
Pregnancy Week-by-Week Calculator
Learn how a pregnancy week-by-week calculator estimates gestational age, pregnancy week, trimester, and due date.