Enter two beta hCG results to calculate your hCG doubling time, percent increase and how your levels compare with typical early-pregnancy ranges.
Human chorionic gonadotropin (hCG) is the hormone produced by the cells that will become the placenta, starting shortly after a fertilized egg implants in the uterus. It is the hormone that home pregnancy tests detect in urine — and the one a quantitative blood test, usually called a beta hCG or simply a "beta," measures precisely in mIU/mL (milli-international units per milliliter).
A single beta tells your provider that hCG is present and roughly how much. But because normal levels vary enormously from person to person and pregnancy to pregnancy, one value on its own says very little. That is why providers often order two draws about 48 hours apart: it is the trend — how quickly hCG is rising — that carries most of the information in very early pregnancy. This calculator does the doubling-time math for you using the standard exponential-growth formula, so you and your provider can look at the same numbers together.
Doubling time is not one fixed number — it naturally slows as hCG climbs. Clinical references such as ACOG and UpToDate describe typical patterns like these:
| Starting hCG level | Typical doubling time |
|---|---|
| Below 1,200 mIU/mL | 48–72 hours |
| 1,200–6,000 mIU/mL | 72–96 hours |
| Above 6,000 mIU/mL | Often more than 96 hours |
These are typical ranges, not cutoffs. Landmark work on hCG curves in viable pregnancies (Barnhart et al., 2004) found that the slowest normal rise can be as low as about 35% over 48 hours — well below "doubling" — which is why a single slower-than-average result is followed up rather than treated as an answer by itself.
This is the question almost everyone actually arrives with, so here it is worked through end to end. Two numbers matter, and they are not the same number.
The doubling figure is simply your result times two: 124 × 2 = 248 mIU/mL two days later. That is the benchmark people repeat, and at a starting level this low a healthy pregnancy often does roughly hit it.
The minimum expected rise is the more clinically useful one. Barnhart's curves put the slowest normal 48-hour rise in a viable intrauterine pregnancy at about 35%. For 124 that is 124 × 1.35 ≈ 167 mIU/mL. So anything from about 167 upward is inside the normal range — a second value of 210 is not a failed double, it is a 69% rise, comfortably normal.
To turn any two results into a percentage yourself: subtract the first from the second, divide by the first, multiply by 100. To convert them into a doubling time, the formula is doubling time = hours between draws × ln(2) ÷ ln(second ÷ first). For 124 → 210 over 48 hours that works out to about 63 hours. The calculator above does both and, importantly, handles draws that were not exactly 48 hours apart — a common source of false alarm, since a 72-hour gap makes a perfectly normal rise look slow if you compare it against a 48-hour benchmark.
Two practical notes. Compare results from the same laboratory where you can — assays are calibrated differently, and a lab switch between draws can invent a change that is not there. And remember that percentages stop being the right lens once hCG is high: past roughly 6,000 mIU/mL, doubling times of 72–96 hours are ordinary, and an ultrasound tells you far more than another blood draw.
If there is one thing to take away from this table, it is how enormous the normal ranges are. At 5 weeks, anything from 18 to 7,340 mIU/mL can be normal — a 400-fold spread. Two people with perfectly healthy pregnancies at the exact same gestational age can have wildly different numbers.
| Weeks since last period | Typical hCG range (mIU/mL) |
|---|---|
| 3 weeks | 5–50 |
| 4 weeks | 5–426 |
| 5 weeks | 18–7,340 |
| 6 weeks | 1,080–56,500 |
| 7–8 weeks | 7,650–229,000 |
| 9–12 weeks | 25,700–288,000 |
Because the ranges overlap so heavily, hCG cannot reliably date a pregnancy, and comparing your number to a friend's — or to a forum post — tells you almost nothing. Whether your value sits at the low or high end of a range matters far less than whether it is rising appropriately for you. The trend matters; the single value mostly does not.
A rise that is slower than the typical ranges above has several possible explanations, and it is worth being honest about all of them. Some ongoing, healthy pregnancies simply rise slowly — particularly as levels get higher, and especially if the pregnancy is a little earlier than dating suggests. At the same time, a slow rise can also be an early sign of a pregnancy that is not progressing, including miscarriage or an ectopic pregnancy (a pregnancy implanted outside the uterus, which needs prompt medical attention).
The important thing is that a slow rise is a reason for follow-up, not a verdict. Your provider will usually repeat the beta in about 48 hours and, once hCG is high enough, use ultrasound — which gives far clearer answers than hCG alone. If you have pain, significant bleeding, shoulder-tip pain or feel faint, contact your provider or emergency services right away rather than waiting for the next blood draw.
Doubling is an early-pregnancy phenomenon. As levels climb into the tens of thousands, the rise flattens out on purpose: hCG typically peaks somewhere around weeks 8 to 11 and then gradually declines to a lower plateau for the rest of pregnancy. If your levels have stopped doubling late in the first trimester, that is the expected pattern — it is not a sign that something has gone wrong. By that stage, providers rely on ultrasound rather than hCG to check on a pregnancy, and repeat betas usually are not useful anymore.
It is completely natural to want one number to tell you whether everything is okay — especially after a loss, or a long time trying to conceive. Unfortunately, hCG cannot do that. Normal ranges span orders of magnitude, labs and assays differ slightly, dating from a last period is often off by days, and twins, implantation timing and simple biology all shift the numbers. A "low" value can be a healthy pregnancy that implanted a bit later; a "high" value is not a guarantee.
What betas do reasonably well is show a trend across two or more draws — and even the trend has a wide normal range. So use this calculator to understand your numbers, bring the results to your appointment, and let your provider put them in the context of your history, symptoms and ultrasound findings. However your numbers look today, you deserve clear information and kind care — and those come from your care team, not from a single lab value.
In many early pregnancies with an hCG level below 1,200 mIU/mL, hCG doubles roughly every 48 to 72 hours. Between 1,200 and 6,000 mIU/mL, doubling often slows to every 72 to 96 hours, and above 6,000 mIU/mL it can take more than 96 hours. These are typical patterns, not rules — some healthy pregnancies rise more slowly, so only your provider can interpret your results.
Yes. Research on hCG curves (Barnhart et al.) found that some viable pregnancies rise as little as about 35% over 48 hours early on. A slower-than-average rise is something your provider will want to follow with repeat labs and possibly an ultrasound, but on its own it does not confirm a problem.
Normal ranges are extremely wide — for example roughly 18 to 7,340 mIU/mL at 5 weeks and 1,080 to 56,500 mIU/mL at 6 weeks. Because the ranges overlap so much, a single value cannot date a pregnancy or predict its outcome. The trend between two draws matters far more than any one number.
Doubling would put it at 248 mIU/mL, but that is a benchmark rather than a requirement. The lowest normal 48-hour rise for a viable intrauterine pregnancy is around 35%, which for 124 is about 167 mIU/mL — so results from roughly 167 upward fall inside the normal range. A second value of 210 is a 69% rise, equivalent to a doubling time of about 63 hours, and entirely typical. If your two draws were not 48 hours apart, compare them using the calculator above rather than against a flat 48-hour benchmark.
Doubling time = hours between the two draws × ln(2) ÷ ln(second result ÷ first result). For 124 rising to 210 over 48 hours, that is 48 × 0.693 ÷ 0.527, or about 63 hours. For a plain percentage rise instead, subtract the first result from the second, divide by the first and multiply by 100. Use results from the same laboratory where possible, since assays are calibrated differently and switching labs between draws can create an apparent change that is not real.
hCG usually stops doubling once levels are high, and it typically peaks around weeks 8 to 11 of pregnancy before declining and leveling off for the rest of pregnancy. A plateau or slow rise late in the first trimester is expected and is not, by itself, a sign that something is wrong.
Contact your healthcare provider and share both values with them. A falling hCG can mean a pregnancy is not progressing, but lab variation and timing can also play a role, and your provider is the only one who can interpret your results in context. You deserve real answers and real support — please reach out to your care team.