About HerCalc

HerCalc is a small toolkit of women's health calculators that take the awkward parts seriously — irregular cycles, PCOS, IVF dating, post-pregnancy body change, perimenopause. Every tool is free, every calculation runs in your browser, and we never ask for an email or sign-up.

Why we built this

Most "women's health calculators" online were built around two assumptions: that every cycle is a clean 28 days, and that every body fits a textbook BMI table. Both assumptions fail more often than they succeed. Cycles vary, ovulation shifts, gestational age methods disagree, and BMI alone misclassifies the cardiometabolic risk for women with the same weight but different waist-to-hip ratios.

HerCalc is our attempt to do the math more honestly. Where a single number is misleading, we show a confidence range. Where a method is unreliable for a given user, we say so out loud. Where a different tool would be a better fit, we link to it.

What makes HerCalc different

• PCOS-aware by default. Our period and ovulation tools have a dedicated PCOS / irregular-cycle mode that adjusts the luteal-phase assumption, widens the fertile buffer, and surfaces relevant warnings instead of pretending everyone ovulates on day 14.
• Multiple methods, transparently compared. Our due-date calculator supports five dating methods (LMP, conception, ultrasound by CRL or weeks+days, IVF day-3/5/6 transfer, and reverse from a known EDD). We tell you which is most reliable for your situation and why.
• Privacy-first. Calculations run entirely on your device. We do not store your last menstrual period, weight, height, or any health input on a server. We use Cloudflare Web Analytics, which is cookieless and aggregate-only.
• Methodologically honest. We cite the formulas behind every calculator (Robinson–Fleming for CRL dating, Naegele's rule for LMP-based EDD, FFIT for body-shape classification, WHR thresholds from WHO 2008) and we link to the studies in our methodology page.

Who we're for

HerCalc is for anyone who menstruates, is trying to conceive, is pregnant, or is paying attention to body composition through a life-stage transition. The tools are most useful for people whose cycles or bodies don't fit the textbook average — irregular periods, PCOS, post-pregnancy, perimenopause, IVF cycles. The content is written in plain English, with the medical accuracy of a clinical reference.

Who we are

HerCalc is built and maintained by a small team of engineers, writers, and contributing clinicians. Our content is editorially reviewed and, where appropriate, medically reviewed before publication. We disclose reviewers on each post. We are not a medical practice, and HerCalc does not replace a clinician — but we work hard to produce information you can trust enough to bring to a clinician.

Editorial standards

We follow the principles of E-E-A-T (Experience, Expertise, Authority, Trust). Each tool page cites the formulas it uses, links to the underlying studies, and notes its limitations. Each blog post that gives clinical guidance is reviewed by a clinician and dated. We update content when guidelines change. Corrections are tracked at the bottom of every post.

Contact

Found a bug, a typo, or a clinical inaccuracy? Have an idea for a calculator we should build? Email hello@hercalc.com. We read everything.