TOOL · HEALTH · PREGNANCY
Pre-pregnancy BMI 23.3 (5 ft 5 in, 140 lb) is in the normal range — so the IOM 2009 target is 25–35 lb total, gained at 0.8–1.0 lb/week in the 2nd and 3rd trimesters. Enter your own numbers below for your personal range, and your current week for the expected-gain-to-date band.
Medical disclaimer: this calculator is informational only and is not medical advice. Weight-gain targets are personal: your clinician may set a different range based on your health, age, and pregnancy. Always follow your doctor’s or midwife’s guidance over any online calculator. If you’re ever concerned about your weight, call your provider.
Enter your pre-pregnancy height and weight, pick singleton or twins, and optionally add your current week. The calculator returns your pre-pregnancy BMI, your BMI category, the IOM 2009 recommended total gain, and the recommended weekly rate — plus expected gain to date if you enter a week.
BMI = 703 × weight(lb) ÷ height(in)². Find your pre-pregnancy BMI category, read the IOM 2009 total-gain range, and gain most of it in the 2nd and 3rd trimesters at the listed weekly rate. At the defaults: BMI = 703 × 140 ÷ 65² = 23.3 → normal → 25–35 lb total, at 0.8–1.0 lb/week in the 2nd and 3rd trimesters.
| Pre-pregnancy BMI | Category | Total gain (singleton) | Weekly rate, 2nd & 3rd trimester | Total gain (twins) |
|---|---|---|---|---|
| < 18.5 | Underweight | 28–40 lb | 1.0–1.3 lb/wk | insufficient data |
| 18.5–24.9 | Normal | 25–35 lb | 0.8–1.0 lb/wk | 37–54 lb |
| 25.0–29.9 | Overweight | 15–25 lb | 0.5–0.7 lb/wk | 31–50 lb |
| ≥ 30.0 | Obese | 11–20 lb | 0.4–0.6 lb/wk | 25–42 lb |
Setup: 65 in tall, 140 lb pre-pregnancy, singleton, week optional.
Line 1 — BMI. 703 × 140 ÷ (65 × 65) = 98,420 ÷ 4,225 = 23.3.
Line 2 — category. 23.3 falls in 18.5–24.9 → normal BMI category.
Line 3 — total gain. Normal + singleton → 25–35 lb total (IOM 2009).
Line 4 — weekly rate. Normal → 0.8–1.0 lb/week during the 2nd and 3rd trimesters.
Branch — expected gain to date at week 20: first trimester (weeks 1–13) brings 1.1–4.4 lb; weeks 14–20 are 7 weeks at 0.8–1.0 lb/wk = 5.6–7.0 lb; total expected by week 20 = 6.7–11.4 lb. Below the range isn’t failure and above isn’t catastrophe — it’s a check-in point with your clinician.
Branch — underweight (BMI 17.5): 28–40 lb total at 1.0–1.3 lb/wk — the highest range, because the baby draws from the same reserves.
Branch — obese (BMI 32): 11–20 lb total at 0.4–0.6 lb/wk — the range is lower but never zero; the baby still needs steady nutrition. Do not attempt to lose weight during pregnancy unless your clinician specifically directs it.
Branch — twins, normal BMI: 37–54 lb total — roughly 12–19 lb more than a singleton. For underweight twin pregnancies the IOM found the evidence insufficient to set a range; your clinician will set one individually.
| Output | Formula | What it means |
|---|---|---|
| Pre-pregnancy BMI | 703 × lb ÷ in² | 23.3 at the defaults — the category key for everything below. |
| BMI category | IOM cutoffs (<18.5 / 18.5–24.9 / 25–29.9 / ≥30) | Normal at the defaults. |
| Recommended total gain | IOM 2009 table by category | 25–35 lb (singleton, normal) at the defaults. |
| Recommended weekly rate | IOM 2009, 2nd & 3rd trimester | 0.8–1.0 lb/wk (singleton, normal) at the defaults. |
| Expected gain to date | 1.1–4.4 lb (1st tri) + rate × (week − 13) | 6.7–11.4 lb at week 20 for the default profile — only shown when a week is entered. |
Ranges come from the Institute of Medicine’s 2009 report “Weight Gain During Pregnancy: Reexamining the Guidelines” (National Academies Press) — the guideline U.S. clinicians still use. It is population guidance, not a prescription: your clinician may adjust for age, height extremes, prior pregnancies, diabetes, hypertension, or other conditions. The twin ranges rest on thinner evidence, and for underweight twin pregnancies the IOM found insufficient data — no range is given, by design. The expected-to-date estimate assumes the first-trimester 1.1–4.4 lb band plus a steady weekly rate; real weight gain fluctuates week to week. BMI is a screening tool, not a body-composition measure. This calculator is informational only — follow your clinician’s guidance.
Bright Side Kit. "Pregnancy Weight Gain Calculator: IOM Weight Ranges 2026." https://brightoolbox.com/pregnancy-weight-gain-calculator/ Accessed October 24, 2026.Data sourcesIt depends on your pre-pregnancy BMI (IOM 2009): underweight 28–40 lb, normal 25–35 lb, overweight 15–25 lb, obese 11–20 lb. Those are total ranges for a singleton. Your clinician may set a different, personal target — theirs wins over the chart.
Very little at first: the IOM’s first-trimester expectation is just 1.1–4.4 lb. Then the weekly rates kick in for the 2nd and 3rd trimesters — 0.8–1.0 lb/wk for a normal BMI, slower for higher BMIs, faster for underweight. Enter your week above for the expected-to-date band.
Yes — roughly 12–19 lb more total: normal BMI 37–54 lb, overweight 31–50 lb, obese 25–42 lb (IOM 2009). One honest gap: for underweight twin pregnancies the evidence was insufficient to set a range, so your clinician sets it individually.
A single weigh-in isn’t the verdict — weight fluctuates with water, meals, and time of day, and the weekly rate is an average, not a weekly quota. A sustained pattern above the range is worth a conversation with your provider, not panic: they’ll look at diet, activity, blood pressure, and glucose together.
Not literally. In the 2nd and 3rd trimesters most people need roughly 300–340 extra calories a day — a snack, not a second dinner — and none extra in the first trimester for most. Quality matters more than quantity: protein, iron, folate, and calcium earn their place; your clinician or dietitian can personalize it.
Not on your own. Even the obese-BMI range is 11–20 lb of gain, never zero and never negative — the baby needs steady nutrition and restricted diets can risk development. If your clinician specifically prescribes a different plan (for example with gestational diabetes), follow their plan, not a calculator’s.