Pregnancy calculator
Pregnancy Weight Gain Calculator
Healthy gain range and weekly target based on your pre-pregnancy BMI and whether you're carrying a singleton, twins, or triplets. Built on the IOM 2009 guidelines used by your obstetrician.
Last reviewed 18 May 2026
How to use this calculator
- Select your pregnancy type: singleton, twins, or triplets.
- Pick units (imperial lb/in or metric kg/cm).
- Enter pre-pregnancy weight and height — that's enough to see your BMI category, total range, and weekly target.
- Optionally enter current weight and pregnancy week to see exactly where you sit on the curve.
- The chart below the results shows the recommended-range envelope across all 40 weeks. If you've entered your current data, a "you are here" dot appears.
Background: the IOM 2009 framework
Singleton ranges (canonical)
| Pre-pregnancy BMI | Total (lb) | Total (kg) | Weekly (T2+T3) |
|---|---|---|---|
| Underweight (<18.5) | 28–40 | 12.5–18 | 1.0–1.3 lb / 0.45–0.59 kg |
| Normal (18.5–24.9) | 25–35 | 11.5–16 | 0.8–1.0 lb / 0.36–0.45 kg |
| Overweight (25–29.9) | 15–25 | 7–11.5 | 0.5–0.7 lb / 0.23–0.32 kg |
| Obese (≥30) | 11–20 | 5–9 | 0.4–0.6 lb / 0.18–0.27 kg |
Twin ranges
The IOM published twin-pregnancy ranges for Normal, Overweight, and Obese BMI categories. The Underweight twin row was not published — the calculator shows a provisional clinical estimate (~50–62 lb / 22.7–28.1 kg) flagged as such in the UI.
| Pre-pregnancy BMI | Total (lb) | Total (kg) |
|---|---|---|
| Underweight (provisional) | 50–62 | 22.7–28.1 |
| Normal (18.5–24.9) | 37–54 | 16.8–24.5 |
| Overweight (25–29.9) | 31–50 | 14.1–22.7 |
| Obese (≥30) | 25–42 | 11.3–19.1 |
Triplet pregnancies
No formal IOM range exists for triplets. Aggregate clinical recommendation is roughly 50–60 lb / 22.7–27.2 kg by 32–34 weeks (typical preterm delivery for triplets). All triplet targets should be individualised by your maternal-fetal medicine team.
How to interpret your results
The chart envelope
The green band on the chart is your gestational-age-adjusted range — i.e., the recommended cumulative gain at each week. T1 (weeks 1–13) is mostly flat because the IOM allows only ~0.5–2 kg total in that period. From week 14 onwards the linear weekly rate determines the slope.
"You are here" dot
When you enter current weight + current week, the calculator places a marker dot on the chart. Inside the green band = on track. Below it = provider conversation about appetite, nausea, undernutrition. Above it = provider conversation about food patterns, fluid retention, glucose.
Status chip
Above the chart, a coloured status chip says one of:
- On track — gain is within the recommended range at your current week.
- Below range — gain is >1 lb below the lower bound at your current week.
- Above range — gain is >1 lb above the upper bound at your current week.
A 1 lb buffer is applied so normal day-to-day fluctuation doesn't trigger a false flag.
Why patterns matter more than single numbers
Weight on any given day is influenced by hydration, time of day, last meal, bowel patterns, and clothing. A single weigh-in can mislead in either direction. Your provider is looking at the trend over weeks. If the line tracks roughly inside the range, that's reassuring. If the line bends sharply up or down, that's a signal worth discussing — because the pattern changed, not because of any one number.
"Eating for two" is a myth
The actual extra energy needs are modest:
- T1: typically no extra calories needed.
- T2: ~+340 kcal/day.
- T3: ~+450 kcal/day (singleton). Twins/triplets need more — discuss with your provider.
Quality matters more than quantity. Iron, folate, calcium, iodine, choline, and omega-3 fatty acids all rise in importance — see the Food Safety Checker and our food guides for specifics.
Limitations — what this calculator does NOT do
- It doesn't diagnose gestational diabetes, hypertensive disorders, or any obstetric complication.
- It doesn't account for fluid retention, pre-existing conditions (thyroid, PCOS), or fetal growth concerns.
- It doesn't replace prenatal visits — weight is just one of many measurements your provider tracks.
- Triplet ranges are aggregate clinical estimates only.
Sources
- Institute of Medicine. Weight Gain During Pregnancy: Reexamining the Guidelines. National Academies Press, 2009.
- American College of Obstetricians and Gynecologists. Committee Opinion No. 548: Weight Gain During Pregnancy. 2013, reaffirmed.
- Goldstein RF et al. Association of gestational weight gain with maternal and infant outcomes: a systematic review and meta-analysis. JAMA. 2017;317(21):2207-2225.
- Society of Maternal-Fetal Medicine (SMFM) Consult Series — recommendations on twin and triplet pregnancy management.
- Luke B, et al. Specialized prenatal care and maternal and infant outcomes in twin pregnancy. American Journal of Obstetrics & Gynecology. 2003 (re: twin-pregnancy weight gain).
Our editorial process is described in our methodology. This calculator is not a substitute for medical advice — read our medical disclaimer.