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Find your recommended total pregnancy weight gain and a target for the current week based on your pre-pregnancy BMI.
Example
A woman is 165 cm tall and weighed 60 kg before pregnancy, now at week 20.
BMI = 60 / (1.65 x 1.65) = 22.0 -> Normal weight
Recommended total gain: 11.5-16.0 kg
Week 20 target (steady gain after week 13):
weeks into 2nd/3rd tri = 20 - 13 = 7 of 27
low = 0.5 + (11.5 - 0.5) x 7/27 = 3.4 kg
high = 2.0 + (16.0 - 2.0) x 7/27 = 5.6 kg
Target by week 20: 3.4-5.6 kg
How it works
Enter your pre-pregnancy height and weight to compute BMI, then your current week of pregnancy. The tool applies IOM recommended gain ranges by BMI category and prorates them to your week.
Good to know
The Pregnancy Weight Gain Calculator turns your pre-pregnancy height and weight into a BMI category, then shows the total weight gain range the Institute of Medicine recommends for a singleton pregnancy in that category. Enter your current week and it also estimates how much of that gain you'd typically have reached by now, so you can see whether you're roughly on track at any point from conception to week 40.
It's aimed at expecting parents and anyone tracking a partner's pregnancy who wants a quick, private reference point between prenatal visits. You'd reach for it when you're curious how your starting BMI shapes the target, when you want to sanity-check a number a midwife mentioned, or when you simply want a week-by-week milestone rather than a single end-of-pregnancy figure. Inputs accept cm/in and kg/lb, and results display in kg or lb, so you don't have to convert anything by hand.
Read the result as two layers. The "recommended total gain" is the full-pregnancy range for your BMI band (for example, 11.5-16 kg for a normal-weight start), while "target by week" prorates that range: little gain is expected through the first trimester, then a steady climb across weeks 14-40. Both are ranges, not exact figures, and being slightly outside them in a single week says far less than the overall trend across several weeks.
A practical caveat: the figures assume a single baby and a known pre-pregnancy weight, so twins, multiples, or a guessed starting weight will skew the output. Weigh yourself under consistent conditions, and treat these numbers as an educational estimate to discuss with your provider rather than a target to chase or restrict toward.
Frequently asked questions
Which guidelines does this calculator use?
It uses the Institute of Medicine (IOM/NAM) recommended total weight gain ranges for singleton pregnancies, set by your pre-pregnancy BMI category: underweight 12.5-18 kg, normal 11.5-16 kg, overweight 7-11.5 kg, and obese 5-9 kg.
How is the target for my current week calculated?
It assumes a small gain of about 0.5-2 kg through the first trimester (week 13), then spreads the remaining recommended gain steadily across weeks 14-40, so your week-specific target is the proportion expected by that point.
Is my data uploaded anywhere?
No — this calculator runs entirely in your browser; nothing is uploaded.
Is this a substitute for medical advice?
No. These are educational estimates — consult a qualified health professional for medical decisions.
People also ask
How much weight should I gain during pregnancy if I started at a normal BMI?
The IOM recommends a total gain of about 11.5 to 16 kg (roughly 25 to 35 lb) for a singleton pregnancy when pre-pregnancy BMI is in the normal range (18.5 to 24.9). The range narrows for higher starting BMI and widens for underweight starts.
Why does pregnancy weight gain depend on pre-pregnancy BMI?
Recommended gain is tied to starting BMI because someone who began underweight is advised to gain more (12.5 to 18 kg) while someone who began with obesity is advised to gain less (5 to 9 kg). The aim is supporting fetal growth while accounting for the parent's existing energy reserves.
Is it normal to gain little or no weight in the first trimester?
Yes, gain is typically small in the first trimester, often only about 0.5 to 2 kg, with most weight added across the second and third trimesters. Nausea or appetite changes can mean minimal or even no early gain for some people.
Does this calculator work for twins or multiple pregnancies?
No. It is built around IOM ranges for singleton pregnancies, and twin or higher-order pregnancies have different, generally higher recommended ranges. A healthcare provider can give targets appropriate for multiples.
What if I don't know my exact pre-pregnancy weight?
The calculation depends on pre-pregnancy weight to set your BMI category, so a rough estimate will produce a rough result. Using your most recent known weight before conception gives the closest approximation; a provider may use measured records instead.
What does the 'target by week' number actually represent?
It is the cumulative amount you'd be expected to have gained by that specific week, not the gain for that week alone. It assumes a small first-trimester gain followed by steady weekly gain through week 40, then shows the proportional range for the week you entered.
Can gaining outside the recommended range be a problem?
Gaining well above or below recommended ranges has been associated in research with various pregnancy outcomes, but individual circumstances vary widely. Any concerns about your weight trend during pregnancy are best evaluated by a qualified health professional.
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