Methodology: How Our Calculators Work

Last updated: July 5, 2026

FeminaTrack's calculators are built to give you clear, useful estimates based on established, widely-used methods. This page explains how each one works, what it's based on, and — just as importantly — what it can't tell you.

Ovulation Calculator

How it works: Estimates your next period date using your last period date and average cycle length, then works backward using your luteal phase length (adjustable, 10–16 days, defaulting to the average of 14) to estimate your ovulation day. Your fertile window is calculated as the 5 days before ovulation plus ovulation day itself — 6 days total — based on the standard convention that sperm can survive up to 5 days while the egg survives 12–24 hours after release.

Limitations: This is an estimate, not a measurement — actual ovulation timing varies between individuals and even cycle to cycle in the same person, and predictions are less precise if your cycle is irregular. If you know your own luteal phase length from prior tracking, entering it improves accuracy; otherwise, methods like basal body temperature charting, LH test strips (OPKs), or medical monitoring give a more precise, confirmed picture than any calendar-based estimate.

Due Date Calculator

How it works: Offers three calculation methods. Last Menstrual Period: adds 280 days to the first day of your last period, adjusted for your actual average cycle length rather than assuming a fixed 28 days. Conception Date: adds 266 days directly from a known conception or ovulation date. Ultrasound: converts your gestational age at the time of the scan into an equivalent last-period date, then applies the same 280-day estimate from that point.

Limitations: Only about 5% of babies are born on their exact estimated due date, and full-term pregnancy spans a five-week range (37–42 weeks), not a single day. Of the three methods, the Last Period method is generally the least precise; an early, first-trimester ultrasound is generally considered the most accurate. Your healthcare provider's own dating always takes precedence over any online estimate.

Period Tracker

How it works: Uses your last period date, average cycle length, and typical period length to project your next 3 periods, and estimates ovulation using a standard 14-day luteal phase assumption. It also identifies which of the 4 cycle phases (menstrual, follicular, ovulation, luteal) you're likely in today.

Limitations: Accuracy depends entirely on how regular your actual cycle is and how accurate your entered history is. It assumes a fixed 14-day luteal phase; if your own luteal phase is meaningfully different, our Ovulation Calculator, which lets you adjust that number, may give a more personalized estimate. This tool should never be relied on as a method of contraception.

hCG Level Calculator

How it works: Offers two modes. Doubling Time: enter two hCG blood test results and their dates, and the calculator determines your actual doubling time and the percentage rise over 48 hours, compared against clinically-cited thresholds. Check My Level: enter a single hCG value and your approximate week of pregnancy, compared against commonly cited reference ranges for that week.

Limitations: hCG reference ranges are extremely wide, and a healthy pregnancy can fall outside them — a single reading is not a reliable indicator on its own, which is why tracking the trend across two tests is generally more informative. Only a healthcare provider tracking your levels over time, alongside other clinical information, can properly interpret hCG results.

Pregnancy Week Tracker

How it works: Works in either direction using the standard 40-week (280-day) pregnancy convention. Enter your current week directly to get a matching due date, or enter your due date to calculate your current week. Each week displays a size comparison, approximate length and weight, and notes on development, symptoms, and a weekly tip.

Limitations: Both directions rely on the same standard 40-week assumption used across our due date tools — this is an estimate, not a clinical measurement. Size, weight, and developmental descriptions are population averages; meaningful variation from these figures is normal.

Fertility Score Quiz

How it works: A 10-question self-assessment covering age, cycle regularity, weight, sleep, stress, exercise, diet, smoking, alcohol/caffeine intake, and supplement use. Each answer carries a weighted point value, summed into a score out of 100 and grouped into one of four bands, each with general lifestyle tips.

Limitations: This is an entirely self-reported lifestyle reflection, not a clinical fertility test — it cannot measure ovarian reserve, hormone levels, sperm quality, or any diagnosable fertility factor, and it does not account for either partner's underlying medical conditions. Use it as a conversation starter with a provider, never as a substitute for actual fertility testing.

Chinese Gender Predictor

How it works: Uses your date of birth and conception date (or month/year) to estimate your Western age at conception, then approximates lunar age by adding one year — a simplified stand-in for the traditional Chinese lunisolar calendar. That lunar age is matched against a traditional gender chart to produce a Boy or Girl prediction.

Limitations: For entertainment purposes only, with no scientific or medical basis — accuracy is consistent with chance, about 50%. Our lunar age conversion is a simplified approximation, not an exact lunisolar calculation. The underlying chart only covers lunar ages 18–45; ages outside that range are matched to the nearest boundary. Should not be used for any medical, legal, or practical decision.

IVF Due Date Calculator

How it works: Offers three modes depending on what you know. Day 3 Transfer: adds 263 days to your transfer date. Day 5 Blastocyst Transfer: adds 261 days. Egg Retrieval Date: adds 266 days, treating retrieval as equivalent to ovulation day. All three follow conventions commonly used by fertility clinics and are designed to produce a consistent due date regardless of which milestone you calculate from.

Limitations: A general estimate based on standard clinical conventions. Your fertility clinic's own dating — based on your specific protocol, embryo grade, and monitoring — is the more authoritative reference. Only about 4–5% of babies are born on their exact estimated due date.

Pregnancy Weight Calculator

How it works: Calculates your pre-pregnancy BMI from your height and weight, then compares it against weight-gain ranges consistent with Institute of Medicine (IOM) guidelines — separate ranges for total pregnancy gain and recommended weekly gain during the second and third trimesters, for both single and twin pregnancies, across four BMI categories.

Limitations: These are population-level reference ranges, not a personalized target — healthy weight gain varies by individual, pregnancy, and underlying health conditions. Always follow your own provider's specific recommendation for your pregnancy.

How We Maintain This Page

As part of our Content Update Policy, we periodically review each calculator's methodology to confirm it still reflects current, widely-accepted conventions, and we update this page if a calculator's underlying method ever changes.

Questions about how a calculator works?

Reach out at hello@feminatrack.com — we're happy to explain further.