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Pregnancy Weight Gain Calculator

Estimate a week-by-week healthy pregnancy weight-gain range from your pre-pregnancy BMI, using Institute of Medicine guidelines for singleton and twin pregnancies.

US Units

ExampleSample values — edit any field to see your result.

Gestational week from the first day of the last period (week 1 through week 40).

Pregnant with twins

Twin pregnancies use a higher IOM total-gain range. Underweight twins reuse the normal-weight twin range.

ft
in
lb
lb

Results update as you type.

Recommended weight this week

Within range

127.3 – 132.3 lb

Estimated result

Recommended gain so far
7.3 – 12.3 lb
How this week compares
Your current weight is in this week's recommended range.
Recommended weight at week 40
145.0 – 155.0 lb
Pre-pregnancy BMI
19.4kg/m²
About these numbers
These ranges follow Institute of Medicine guidelines for most singleton and twin pregnancies. Gain varies from person to person — a prenatal care provider can tailor the numbers to you.

Week-by-week recommended range

WeekRecommended weightRecommended gain
Week 1120.0 – 120.0 lb0 – 0 lb
Week 2120.1 – 120.4 lb0.09 – 0.4 lb
Week 3120.2 – 120.7 lb0.2 – 0.7 lb
Week 4120.3 – 121.1 lb0.3 – 1.1 lb
Week 5120.4 – 121.5 lb0.4 – 1.5 lb
Week 6120.5 – 121.8 lb0.5 – 1.8 lb
Week 7120.5 – 122.2 lb0.6 – 2.2 lb
Week 8120.6 – 122.6 lb0.6 – 2.6 lb
Week 9120.7 – 122.9 lb0.7 – 2.9 lb
Week 10120.8 – 123.3 lb0.8 – 3.3 lb
Week 11120.9 – 123.7 lb0.9 – 3.7 lb
Week 12121.0 – 124.0 lb1.0 – 4.0 lb
Week 13121.1 – 124.4 lb1.1 – 4.4 lb
Week 14122.0 – 125.5 lb2.0 – 5.5 lb
Week 15122.9 – 126.7 lb2.9 – 6.7 lb
Week 16123.8 – 127.8 lb3.8 – 7.8 lb
Week 17124.6 – 128.9 lb4.6 – 8.9 lb
Week 18125.5 – 130.1 lb5.5 – 10.1 lb
Week 19126.4 – 131.2 lb6.4 – 11.2 lb
Week 20127.3 – 132.3 lb7.3 – 12.3 lb
Week 21128.2 – 133.5 lb8.2 – 13.5 lb
Week 22129.1 – 134.6 lb9.1 – 14.6 lb
Week 23130.0 – 135.7 lb10.0 – 15.7 lb
Week 24130.8 – 136.9 lb10.8 – 16.9 lb
Week 25131.7 – 138.0 lb11.7 – 18.0 lb
Week 26132.6 – 139.1 lb12.6 – 19.1 lb
Week 27133.5 – 140.3 lb13.5 – 20.3 lb
Week 28134.4 – 141.4 lb14.4 – 21.4 lb
Week 29135.3 – 142.5 lb15.3 – 22.5 lb
Week 30136.1 – 143.7 lb16.1 – 23.7 lb
Week 31137.0 – 144.8 lb17.0 – 24.8 lb
Week 32137.9 – 145.9 lb17.9 – 25.9 lb
Week 33138.8 – 147.1 lb18.8 – 27.1 lb
Week 34139.7 – 148.2 lb19.7 – 28.2 lb
Week 35140.6 – 149.3 lb20.6 – 29.3 lb
Week 36141.5 – 150.5 lb21.5 – 30.5 lb
Week 37142.3 – 151.6 lb22.3 – 31.6 lb
Week 38143.2 – 152.7 lb23.2 – 32.7 lb
Week 39144.1 – 153.9 lb24.1 – 33.9 lb
Week 40145.0 – 155.0 lb25.0 – 35.0 lb
Recommended weight this week127.3 – 132.3 lb

Enter your pregnancy week, height, weight before pregnancy, and weight now to see a recommended gain range for this week and at week 40. The schedule follows Institute of Medicine guidelines based on pre-pregnancy BMI, for a singleton or twin pregnancy, in US or metric units.

Formula

Pre-pregnancy BMI is the usual adult formula. That BMI picks an IOM total gain. The weekly schedule is piecewise linear in pounds (metric results convert those pound gains):

BMI = weight (kg) / height (m)²

week 1:   gain = 0
week 13:  gain = 1.1–4.4 lb   (0.5–2 kg)
week 40:  gain = IOM total for your BMI band
week 2–12 and 14–39: straight-line interpolation

recommended weight = pre-pregnancy weight + gain

A weight on either edge of this week's 1-decimal range counts as in range.

Weight gain in pregnancy is expected and useful — it supports the baby, placenta, amniotic fluid, extra blood, and milk stores. These numbers are a planning range, not a grade. A clinician who knows your history can set a more personal goal.

IOM total gain by pre-pregnancy BMI

Pre-pregnancy BMICategorySingletonTwins
Below 18.5Underweight28–40 lb37–54 lb (limited data)
18.5–24.9Normal Weight25–35 lb37–54 lb
25.0–29.9Overweight15–25 lb31–50 lb
30.0 and aboveObese11–20 lb25–42 lb

The first-trimester window (about 1–4 lb / 0.5–2 kg) is the same in every band. From week 14 onward the weekly pace is whatever is left to reach the total by week 40.

Where the extra weight goes

Most of the gain is not the baby alone. Typical contributions by the end of pregnancy are on the order of 1–3 lb in breast tissue, about 2 lb in the uterus, 1.5 lb placenta, 2 lb amniotic fluid, 3–4 lb extra blood, 2–3 lb extra fluid, and 6–8 lb of energy stores for breastfeeding.

Examples

5 ft 6 in, 120 lb before, 130 lb at week 20

Pre-pregnancy BMI is 19.4 (Normal Weight). The week-20 range is 127.3 – 132.3 lb (7.3 – 12.3 lb of gain so far), so 130 lb is inside the band. By week 40 the recommended weight is 145.0 – 155.0 lb (25–35 lb total).

165 cm, 50 kg before, 55 kg at week 20

BMI is 18.4 (Underweight). The week-20 range is 53.7 – 56.2 kg, and the week-40 range is 62.7 – 68.1 kg (about 28–40 lb of total gain, shown in kilograms).

Frequently asked questions

How much weight is recommended during pregnancy?
Institute of Medicine guidelines depend on pre-pregnancy BMI. For a singleton pregnancy the usual totals are 28–40 lb if underweight, 25–35 lb at a typical BMI, 15–25 lb if overweight, and 11–20 lb at BMI 30 or higher. Twin pregnancies use a higher range. These are population ranges, not a personal target — a prenatal care provider can adjust them.
How is the week-by-week range calculated?
Recommended gain starts at 0 in week 1, reaches 1.1–4.4 lb (about 0.5–2 kg) by week 13, then rises in a straight line to the IOM total at week 40. Each week's recommended weight is your pre-pregnancy weight plus that gain. The calculator compares the weight you enter now with that week's range.
Why does pre-pregnancy BMI matter?
The IOM ranges are keyed to BMI from height and weight before pregnancy (or at the first prenatal visit, before much pregnancy-related gain). Underweight, typical, overweight, and BMI-30+ bands have different totals because studies found better outcomes inside those windows — enough stored nutrients without extra strain on labor and recovery.
What if I am pregnant with twins?
Twin pregnancies usually involve more gain. This calculator uses 37–54 lb for a typical BMI, 31–50 lb if overweight, and 25–42 lb at BMI 30 or higher. IOM did not publish a separate underweight-twin range, so that case reuses 37–54 lb — the same choice calculator.net makes. Triplets and higher are not covered here.
What if my weight is outside this week's range?
A single reading above or below the band is a prompt to talk with your care provider, not a diagnosis. Appetite, swelling, and the scale all move from week to week. The useful picture is the trend across visits, alongside how you feel and how the baby is growing.

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