Pregnancy Weight Gain Calculator
Enter your pre-pregnancy weight and height to see the recommended total weight gain for your pregnancy, based on your BMI. Add your current week to see how much is typical by now, and your gain so far to check whether you’re on track.
Enter your pre-pregnancy weight and height to see your recommended gain. Add your current week to see how much is typical by now.
Recommended weight gain by BMI
The widely used guidance comes from the Institute of Medicine (IOM/NASEM), and it’s keyed to your pre-pregnancy BMI — because the healthiest amount to gain depends on where you started. For a single baby:
| Pre-pregnancy BMI | Recommended total gain |
|---|---|
| Underweight (under 18.5) | 28–40 lb (13–18 kg) |
| Healthy weight (18.5–24.9) | 25–35 lb (11–16 kg) |
| Overweight (25–29.9) | 15–25 lb (7–11 kg) |
| Obese (30 or over) | 11–20 lb (5–9 kg) |
Twin pregnancies have higher ranges (about 37–54 lb at a healthy weight) — tick the twins box to use them.
How the weight builds over time
Weight gain isn’t spread evenly. In the first trimester the baby is tiny, so most people gain just 1 to 4.5 lb in total — and some lose a little to morning sickness, which is usually fine. From around week 13, gain settles into a steadier weekly pattern:
- Healthy weight: about 1 lb a week in the second and third trimesters.
- Underweight: a little more, around 1–1.3 lb a week.
- Overweight or obese: less, around 0.5 lb a week.
That’s why this calculator gives both a full-pregnancy total and a “by this week” figure: the second tells you whether your pace right now is roughly where it usually is for your starting BMI.
Where the weight goes
It can be reassuring to remember that pregnancy weight isn’t all baby. A typical gain is shared between the baby (around 7–8 lb at term), the placenta, amniotic fluid, a larger uterus and breasts, extra blood and body fluid, and some fat stores that help support breastfeeding. So the number on the scale reflects a lot of healthy, temporary changes — most of which leave again after the birth.
A note on accuracy
These ranges are general guidance, not a personal prescription. Your provider may set a different target based on your health, how the pregnancy is progressing, or conditions like gestational diabetes. Please don’t try to lose weight or restrict eating in pregnancy unless your provider specifically advises it — the aim is steady, healthy gain, not a number to hit exactly. Use this as a friendly check-in, and bring any concerns about your weight to your appointments.
Frequently asked questions
- How much weight should I gain during pregnancy?
- It depends on your pre-pregnancy BMI. The Institute of Medicine ranges for a single baby are: underweight (BMI under 18.5) 28–40 lb; healthy weight (18.5–24.9) 25–35 lb; overweight (25–29.9) 15–25 lb; and obese (30+) 11–20 lb. For twins the ranges are higher — roughly 37–54 lb at a healthy weight. These are general guides; your provider sets your individual target.
- How is pregnancy weight gain spread across the trimesters?
- Most people gain only a little in the first trimester — about 1 to 4.5 lb total — because the baby is still tiny. Gain then picks up to a fairly steady weekly rate in the second and third trimesters: roughly 1 lb a week at a healthy starting weight, and less (about 0.5 lb a week) if you started overweight or obese. That's why this calculator shows both a total and a 'by this week' figure.
- Why does my pre-pregnancy BMI matter?
- Because the healthiest amount to gain differs depending on where you started. Someone who began underweight is advised to gain more to support the baby, while someone who began with a higher BMI is advised to gain less, since they already carry extra energy stores. Tailoring the target to BMI is linked to better outcomes for both parent and baby, which is why every official range is keyed to it.
- What if I'm gaining too much or too little?
- A single week outside the range usually isn't a concern — weight naturally fluctuates with fluid, food, and time of day. What matters is the overall trend over several weeks. If you're consistently well above or below the typical range, it's worth raising with your provider, who can check whether anything needs adjusting in diet, activity, or monitoring. Don't diet to lose weight in pregnancy unless your provider specifically advises it.
- Is this calculator accurate for twins?
- It uses the IOM provisional ranges for twin pregnancies, which are higher than for a single baby. Tick the 'twins' box to switch to them. There's no formal IOM range for underweight twin pregnancies, so we fall back to the healthy-weight twin range, as published guidance does. As always, twin pregnancies are followed closely, so your provider's target takes priority.
Related calculators
- How Far Along Am I? — your current week and trimester
- Pregnancy Week by Week — what’s happening at each stage
- Pregnancy Due Date Calculator — estimate your due date
- Pregnancy Safety A–Z — what’s safe to eat, do, and take
— The Period Tools Team