A walkthrough, end to end.
- 1
Enter your pre-pregnancy weight, height, and current week of pregnancy.
- 2
The calculator finds your pre-pregnancy BMI and looks up the IOM/NAM recommended range for total gain.
- 3
You'll see total recommended gain, gain so far (if you enter current weight), and a weekly target for the rest of your pregnancy.
IOM 2009 / reaffirmed 2023 guidelines
The Institute of Medicine (now NAM) ranges are based on pre-pregnancy BMI. Underweight: 28–40 lb. Normal: 25–35 lb. Overweight: 15–25 lb. Obese: 11–20 lb. The first trimester contributes only about 1–4 lb; most gain happens in the 2nd and 3rd trimesters at roughly 0.5–1 lb/week.
What you can do with this.
Healthy weight gain by BMI category
Underweight pregnant people are advised to gain more (28–40 lb total); those with obesity less (11–20 lb). Outside-range gain is associated with higher risks of complications either way.
Weekly weight gain target in second/third trimester
After ~13 weeks, the typical recommendation is ~1 lb/week (normal BMI), 0.5 lb/week (obese), or up to 1.3 lb/week (underweight). Daily fluctuation is normal — weigh weekly at the same time of day.
Twin pregnancy weight gain
Twins have higher targets: 37–54 lb (normal BMI), 31–50 lb (overweight), 25–42 lb (obese). This calculator uses singleton ranges — adjust upward if carrying multiples per provider guidance.
What if you've gained too much or too little?
Don't try to lose weight during pregnancy unless directed by your provider. Slow excessive gain by reviewing diet quality with your provider; concerning under-gain may need a nutrition referral.
Frequently asked.
Twin ranges are higher (typically +12 lb above singleton recommendations). Talk to your provider — this calculator uses singleton IOM ranges.
Yes — only ~1–4 lb is expected. Most gain happens after 13 weeks at ~0.5–1 lb/week depending on starting BMI.
Weekly is enough. Daily weight fluctuates 1–3 lb from water alone, which can be discouraging for no real reason.
Both over- and under-gaining have risks. Discuss with your provider — small course corrections in diet quality matter more than chasing the exact number.