Pregnancy Weight Gain Calculator
Weight Gain Isn't Meant to Be Linear
Total pregnancy weight gain guidance gets quoted often, but the pacing matters just as much as the total — very little is expected in the first trimester, and the bulk arrives steadily afterward. Comparing your current weight against the full-pregnancy target alone can be misleading at week 10 or week 34; this calculator instead paces the target by how far along you are, so the comparison is against what's expected by that specific week.
The Formula
BMI = Pre-pregnancy Weight (kg) ÷ Height (m)²
Expected fraction of total gain by week ≤13: (week ÷ 13) × 0.10
Expected fraction of total gain by week >13: 0.10 + ((week − 13) ÷ 27) × 0.90
The pacing model allocates roughly 10% of total recommended gain to the first 13 weeks, then spreads the remaining 90% roughly evenly from week 13 through week 40 — reflecting how modest early gain typically is compared with the second and third trimesters.
Expected Gain-to-Date by Week
For someone in the normal pre-pregnancy BMI category (total target 25–35 lb):
| Week | Expected gain to date |
|---|---|
| Week 8 | 1.5 – 2.2 lb |
| Week 13 | 2.5 – 3.5 lb |
| Week 20 | 8.3 – 11.7 lb |
| Week 28 | 15.0 – 21.0 lb |
| Week 32 | 18.3 – 25.7 lb |
| Week 36 | 21.7 – 30.3 lb |
| Week 40 | 25.0 – 35.0 lb |
Computed with the calculator's own pacing formula. Other BMI categories use the same pacing curve applied to their own total range (see the underlying Pregnancy Weight Calculator for the four IOM ranges).
Reading Your Result
- Within range — your gain-to-date sits inside the paced expectation for your BMI category and current week.
- Below range — worth mentioning at your next appointment, particularly in the second and third trimesters when steady gain matters for fetal growth.
- Above range — also worth discussing; a single high or low week is rarely a concern on its own, but a persistent trend is what providers actually track.
How to Use This Calculator
- Choose Metric (cm / kg) or Imperial (in / lb) units.
- Enter your Height and Pre-pregnancy Weight.
- Enter your Current Weight.
- Enter your Current Week of Pregnancy (0–42).
- Select Calculate for your weight gained so far, your recommended total range, the expected range by this week, and whether you're currently within it.
Related Calculations
For your full-pregnancy target range without the weekly pacing, see the Pregnancy Weight Calculator. To confirm which week you're actually in, use the Pregnancy Week Calculator.