Pregnancy weight gain calculator
Recommended gain depends on your weight before pregnancy, not your weight now. This gives the range for your pre-pregnancy BMI band, what it works out to by your current week, and where you sit against it.
- Against the guideline
- Within the range
- Expected range by this week
- 7.6 – 12.1 lb
- Recommended total gain
- 25.4 – 35.3 lb
- Pre-pregnancy BMI
- 23.3
- BMI band
- Normal
- Weekly rate, second and third trimester
- 0.77 – 1.1 lb
Population guidance, not personal advice. Pregnancy weight is monitored by your midwife or doctor, whose guidance takes precedence over any range shown here.
The formula
Ranges follow the Institute of Medicine's 2009 guidelines by pre-pregnancy BMI: under 18.5, 12.5–18 kg; 18.5–24.9, 11.5–16 kg; 25–29.9, 7–11.5 kg; 30 and over, 5–9 kg. The first trimester accounts for only 0.5–2 kg; the rest accrues at the weekly rate from week 14.
Worked example
At 63 kg and 165 cm before pregnancy, the BMI was 23.1 — the normal band, so 11.5 to 16 kg in total. By week 20, that is 3.5 to 5.5 kg, and a 6 kg gain would sit just above the range.
How to use it
- 1Use your weight before pregnancy, not at your first appointment, if you know it.
- 2Weigh yourself at the same time of day, on the same scales, for a comparable figure.
- 3Treat the range as a guide across the whole pregnancy. Week-to-week variation is normal and means little on its own.
Questions people ask
I am outside the range. Is that a problem?
Not necessarily. The guidelines are population averages for singleton pregnancies, and plenty of healthy pregnancies fall outside them. It is worth mentioning at your next appointment rather than acting on alone.
Does this work for twins?
No. Twin pregnancies have separate, higher ranges — roughly 17 to 25 kg for a normal pre-pregnancy BMI. Ask your midwife for the figures that apply to you.
Last reviewed: 2026-10-20