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hCG Doubling Time Calculator

Compute the doubling time and percentage rise between two hCG results, read against the expected range for the level reached.

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hCG Doubling Time Calculator works straight from this page — free, instant, nothing to install. Its place is under Pregnancy & baby; Blood Donation Time Calculator and Baby Growth Percentile Calculator answer the questions closest to this one.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What is hCG Doubling Time Calculator?

Compute the doubling time and percentage rise between two hCG results, read against the expected range for the level reached.

When would I actually use this?

Placing a pregnancy on the calendar: the estimated due date, the current week, and when the usual appointments and screenings fall.

What is the most common mistake?

Reading the due date as a deadline. It is a median: fewer than one birth in twenty happens on it, and a normal term spans several weeks around it.

How is hCG Doubling Time Calculator different from Blood Donation Time Calculator?

They sit next to each other but answer different questions: Blood Donation Time Calculator is the one to open when you need it to find your next eligible donation date by donation type, using either the American Red Cross or the French EFS intervals. Pick whichever matches what you're starting from — both are free.

Is there a tool for the next step?

Baby Growth Percentile Calculator is the closest one after this: Weight, length and head circumference percentiles from the WHO Child Growth Standards, 0-24 months.

What else is worth having open alongside it?

Baby Milk Intake Calculator and Gestational Age Calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

The doubling time between two measurements, read against the published expected ranges rather than against the folklore that hCG always doubles in 48 hours — it does so early and slows down markedly as the level rises. The tool also shows the minimum rise obstetricians use in practice: about +53% over 48 hours in the Barnhart 2004 curve, revised down to +35% by the slowest curve of Seeber and Barnhart 2006. Below that, a normal intrauterine pregnancy becomes unlikely — which is a reason to be seen, not a diagnosis. Two numbers on a page cannot distinguish an ectopic pregnancy from a miscalculated date; an ultrasound and a clinician can.

Further reading

All guides →
ExplainerhCG Doubling Time, and What a Single Number Cannot Tell YouDoubling time is ln(2) times the interval divided by the natural log of the ratio. Here it is derived and worked on real pairs, with the two things most often got wrong online: the expected rate slows as the level rises, and a single value is meaningless because the reference range at one gestational week can span more than two hundredfold.ExplainerImplantation Timing and the Window That Decides a Test ResultHow early you can test is the sum of three delays: when implantation happens, how fast hCG climbs from that moment, and what the test can detect. Each one is measured in the literature, so the chain can be computed end to end — and it explains exactly why an early negative is so often wrong.ExplainerWhat Is a Normal Menstrual Cycle Length? The Numbers, by Life StageFIGO puts a normal cycle at 24 to 38 days; ACOG's older range is 21 to 35. Here is why two respected bodies give different numbers, how much variation is normal, and how cycles change after menarche and before menopause.ExplainerHow Much Milk Does a Baby Need? The Rule of Thumb and Its LimitsA formula-fed baby takes roughly 2.3 fl oz per pound of body weight per day in the first months, split across the day's feeds. Here is the table by age and weight, why breastfed babies are not measured this way, and the signs that outrank any number.How-toHow to Predict Your Next Period (And How Far Off the Estimate Can Be)Add your average cycle length to the first day of your last period. Here is how to measure that length properly, why the estimate has a range rather than a date, and when irregularity is worth a consultation.ExplainerIVF Dating Is the One Case Where the Date Is Actually KnownEvery other pregnancy is dated from an estimate. After IVF, fertilisation is timed to the hour, so gestational age is arithmetic: 266 days from fertilisation, minus the embryo's age at transfer. Here is the derivation for day-3, day-5 and day-6 embryos, why frozen and fresh transfers use the same rule, why an early scan rarely moves an IVF date, and what the two-week offset on a scan report means.