HerCalc blog
Plain-English, evidence-based reading on cycle health, fertility, pregnancy, and PCOS — by the same team behind the calculators, with input from contributing clinicians.
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Weight and Fertility: What the Evidence Actually Says
The U-shaped fertility curve, why 5–10% weight changes can restore ovulation, BMI thresholds and time-to-conception, and when weight is and isn't the issue.
Apr 27, 2026 · medically reviewed
safe period
Why the Safe-Period Method Fails One in Four Users (and What Works Better)
Calendar-based fertility awareness has a 24% per-year typical-use failure rate. Here's the data, the math, and what to use instead if pregnancy prevention is the goal.
Apr 25, 2026 · medically reviewed
pregnancy
Calculating Your Due Date by Ultrasound (CRL): A Plain-English Guide
First-trimester ultrasound is the most accurate way to date pregnancy. Here's exactly how the CRL measurement becomes a due date — and when to trust it over your LMP.
Apr 22, 2026 · medically reviewed
fertility
BBT vs LH vs Mucus: Honest Comparison of Ovulation Tracking Methods
How basal body temperature, LH tests, and cervical mucus actually compare for tracking ovulation: cost, accuracy, real-time vs retrospective, and when to combine them.
Apr 19, 2026 · medically reviewed
cycle health
Your Cycle Is a Vital Sign: What Length, Variability & Flow Tell a Clinician
ACOG calls the menstrual cycle a vital sign. Here's how to read your own cycle data the way a clinician would — what counts as normal, what to flag, and what to bring to your next appointment.
Apr 18, 2026 · medically reviewed
pcos
PCOS-Friendly Cycle Tracking: When the Calendar Method Breaks (and What to Do)
Calendar-based cycle prediction routinely fails for PCOS users. Here is a practical, evidence-based playbook for tracking irregular cycles and identifying ovulation when textbook math gives up.
Apr 15, 2026 · medically reviewed
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BMI for Women: What the Number Means, What It Doesn't, and the Context That Matters
BMI for women treats every body the same. Here's what the number actually measures, where it falls short, and the cardiometabolic context (WHR, WHtR, body fat) that gives a fuller picture.
Apr 12, 2026 · medically reviewed
pcos
PCOS Rotterdam Criteria, Explained: How Diagnosis Actually Works
The Rotterdam 2003 criteria for PCOS, how AE-PCOS differs, what each criterion means in practice, and why PCOS diagnosis is genuinely hard.
Apr 11, 2026 · medically reviewed
fertility
The Fertile Window, Explained: Six Days That Matter for Conception
The fertile window is six days, not just one. Here's the Wilcox NEJM 1995 study, what each day means for conception probability, and why early-window timing matters more than people think.
Apr 8, 2026 · medically reviewed
pregnancy
Pregnancy Symptoms by Week: What's Normal, What's Not
A week-by-week guide to pregnancy symptoms from week 4 to week 40 — when each symptom appears, what causes it, and when to call your provider. Based on ACOG guidance.
Apr 8, 2026 · medically reviewed
pregnancy
Twin Pregnancy Due Dates: Why 40 Weeks Is Not the Target
Twin pregnancy gestational targets, ACOG guidance for monochorionic vs dichorionic twins, why 35–37 weeks is typical, and IOM weight gain ranges for twin pregnancies.
Apr 5, 2026 · medically reviewed
cycle health
Hypothalamic Amenorrhea: Why Your Period Disappeared
Hypothalamic amenorrhea causes missing periods through energy deficit, over-exercise, or stress. Learn how it differs from PCOS, how recovery works, and what it means for fertility.
Apr 2, 2026 · medically reviewed
body
Waist-to-Height Ratio: A Better Health Metric Than BMI
Waist-to-height ratio predicts cardiovascular disease, diabetes, and mortality better than BMI. Learn the Ashwell 2012 evidence, how to measure correctly, and what each band means clinically.
Mar 28, 2026 · medically reviewed
pcos
PCOS and Fertility: What to Expect and When to Seek Help
PCOS is the leading cause of anovulatory infertility. Learn how PCOS affects fertility, what labs to get, and how ovulation induction with letrozole or clomiphene works — with 2023 Monash guidance.
Mar 24, 2026 · medically reviewed
pregnancy
Pregnancy Test Timing: When to Test and Why Missed Period Day Wins
When to take a home pregnancy test, hCG doubling rules, sensitivity differences between brands, and why the morning of your missed period is the safe bet.
Mar 22, 2026 · medically reviewed
pregnancy
First Trimester: Weeks 1–13 Milestones and What to Expect
What's developing in weeks 1–13, which symptoms are normal, when your first prenatal visit happens, and what NIPT involves — an honest, ACOG-grounded first trimester guide.
Mar 19, 2026 · medically reviewed
cycle health
Postpartum Period Return: When Cycles Come Back After Birth
When your period returns after birth, how breastfeeding delays it, the LAM method's actual effectiveness, and when to be concerned about postpartum bleeding patterns.
Mar 17, 2026 · medically reviewed
body
BMI vs Body Fat Percentage: When the Number Is Misleading
BMI is a population-level screening tool, not an individual measure. Here is what body fat percentage adds, what 'skinny fat' really means, and which test is worth doing.
Mar 15, 2026 · medically reviewed
pregnancy
IVF Due Date Explained: Day 3, Day 5, and Frozen Transfers
IVF due dates are calculated differently than natural pregnancies. Learn the math for Day 3, Day 5, and Day 6 transfers — fresh and frozen — and why IVF dating is more accurate than ultrasound.
Mar 14, 2026 · medically reviewed
fertility
How to Track Basal Body Temperature for Conception
BBT charting confirms ovulation and reveals your cycle's true pattern. Learn the equipment, technique, and chart interpretation that make BBT useful for conception planning.
Mar 10, 2026 · medically reviewed
pregnancy
Gestational Age vs Fetal Age: The 2-Week Offset Explained
Why your provider says you are 8 weeks pregnant when conception was only 6 weeks ago. The LMP-based gestational age system, in plain language.
Mar 8, 2026 · medically reviewed
cycle health
Perimenopause Cycle Changes: STRAW+10 Staging in Plain English
What happens to your cycle from age 35 onward, the STRAW+10 staging system, hormonal changes in perimenopause, and when irregular is normal vs concerning.
Mar 8, 2026 · medically reviewed
pcos
Anovulation and Irregular Cycles: What's Happening and What to Do
Anovulation means no egg is released, yet bleeding still occurs. Learn to recognize it, understand PCOS links, and know when to see a clinician. Evidence-based guidance.
Mar 5, 2026 · medically reviewed
fertility
Cervical Mucus Tracking: The Most Honest Real-Time Fertility Signal
How cervical mucus changes through your cycle, what dry, sticky, creamy, and egg-white mean, and why mucus is the most accurate real-time marker of fertility.
Mar 3, 2026 · medically reviewed
fertility
AMH and Ovarian Reserve: What the Number Actually Tells You
AMH measures egg quantity, not quality. It does not predict natural fertility well. Here is what AMH means by age, and where it actually matters clinically.
Mar 2, 2026 · medically reviewed
pregnancy
Miscarriage Rates by Week: What the Data Actually Show
A clear, gentle look at miscarriage probability by gestational week, why early ultrasound matters, and what an 80 percent risk reduction by week 8 really means.
Feb 25, 2026 · medically reviewed
cycle health
Stress and Missed Periods: When It Is Actually Stress
Stress can delay or cancel ovulation through HPA axis suppression of GnRH. Here is when stress explains a missed period and when something else is going on.
Feb 19, 2026 · medically reviewed
cycle health
Thyroid and Menstrual Cycles: When and How to Test
Hypothyroidism and hyperthyroidism both shift menstrual cycles. Here is how each one changes your pattern, when to ask for a TSH, and what the labs mean.
Feb 14, 2026 · medically reviewed
cycle health
Endometriosis and Your Cycle: What Patterns to Notice Early
Heavy painful periods are not normal. Endometriosis takes 7 to 10 years to diagnose on average. Here are the cycle patterns and red flags that should prompt earlier evaluation.
Feb 9, 2026 · medically reviewed
fertility
Luteal Phase Defect: What ASRM Actually Says in 2026
Luteal phase defect was once a routine infertility diagnosis. ASRM no longer considers it a clinical entity in most cases. Here is what the evidence actually shows.
Feb 4, 2026 · medically reviewed
body
Waist Circumference: How to Measure and Why It Matters More Than Weight
How to measure waist correctly, WHO and IDF cutoffs (88cm general, 80cm for many Asian populations), and why visceral fat is the metabolic story.
Jan 30, 2026 · medically reviewed
cycle health
Secondary Amenorrhea: Why Your Periods Stopped and What to Investigate
Workup for periods that stopped after being normal: pregnancy first, then PCOS, hypothalamic, thyroid, prolactin, and POI. When to refer.
Jan 27, 2026 · medically reviewed
cycle health
Heavy Menstrual Bleeding: When It Is HMB and What to Do
Defining heavy menstrual bleeding with PBAC and product soak-through, iron-deficiency screening, and the evidence-based evaluation pathway.
Jan 25, 2026 · medically reviewed
pcos
PCOS and Mental Health: Why Anxiety and Depression Are More Common
Anxiety and depression rates are 3x higher in PCOS. The biology, the stigma, and what actually helps when both metabolic and mental symptoms overlap.
Jan 22, 2026 · medically reviewed
pcos
PCOS and Insulin Resistance: Why It Drives Symptoms and What Helps
How insulin resistance fuels PCOS hyperandrogenism, what HOMA-IR means, and the evidence for metformin and lifestyle interventions.
Jan 19, 2026 · medically reviewed
pregnancy
Prenatal Vitamins: What the Evidence Actually Supports
Folic acid timing, iodine, DHA, iron, and the truth about premium prenatals. Evidence-based guidance on what to take and when.
Jan 17, 2026 · medically reviewed
pregnancy
Gestational Diabetes Screening: One-Step vs Two-Step and What to Expect
GDM screening at 24-28 weeks, one-step vs two-step glucose tolerance testing, who needs early screening, and what the numbers mean.
Jan 14, 2026 · medically reviewed
pregnancy
Labor Induction: When It Helps, When to Wait, and What the ARRIVE Trial Showed
Why labor is induced, what 39-week elective induction in low-risk pregnancy actually changes, Bishop score, and how to think about timing.
Jan 11, 2026 · medically reviewed
pregnancy
VBAC Success Rates: Who Is a Good Candidate and What Predicts Success
Vaginal birth after cesarean candidates, predictors of success, the MFMU calculator, and current ACOG guidance for safe trial of labor.
Jan 8, 2026 · medically reviewed
pregnancy
Group B Strep in Pregnancy: Screening, Treatment, What to Know
GBS screening at 36-37 weeks, what a positive result means, intrapartum antibiotics, and current ACOG guidance for safer deliveries.
Jan 5, 2026 · medically reviewed