Pregnancy Weight Gain Calculator · Practical guide
Pregnancy Weight Gain by Week
Most gain happens after week 12 — here is the week-by-week pattern the guidelines expect.
At a glance
The Pattern in One Sentence
Gain 1–5 lb through week 12, then add weight at a steady weekly rate — about 0.5–1 lb per week for a normal pre-pregnancy BMI — through week 40.
Interactive tool
Pregnancy Weight Gain Calculator
Enter your own values, then compare the result with the examples below.
Weight Gain Recommendations
Weekly Chart for a Normal BMI
The ranges below apply the IOM guideline of 1–5 lb in the first trimester followed by 0.5–1 lb per week, the same math the calculator uses:
| Week | Expected Total Gain | Week | Expected Total Gain |
|---|---|---|---|
| 12 | 1–5 lb | 28 | 9–21 lb |
| 16 | 3–9 lb | 32 | 11–25 lb |
| 20 | 5–13 lb | 36 | 13–29 lb |
| 24 | 7–17 lb | 40 | 15–33 lb |
Weekly Rates for Other BMI Categories
After week 12, the weekly rate depends on your pre-pregnancy BMI: underweight women gain 1.0–1.5 lb per week, normal weight 0.5–1.0 lb, overweight 0.4–0.6 lb, and obese 0.3–0.5 lb. An underweight mother at week 28, for example, would expect roughly 17–29 lb of total gain.
When the Scale Surprises You
A single weigh-in can swing 2–3 lb with fluids and meals, so judge your trend over two to four weeks rather than one reading. If your running total sits well above or below the chart for several weeks, bring it up at your next prenatal visit — the goal is a steady trajectory, not hitting an exact number each week.
Frequently Asked Questions
Why does the chart barely move before week 12?
The baby weighs only a few ounces in the first trimester, so guidelines call for just 1–5 lb total. Meaningful gain begins once growth accelerates in the second trimester.
What week does weight gain speed up?
Right after the first trimester. From week 13 onward, guidelines expect a steady weekly gain of 0.5–1 lb for normal-BMI mothers through the rest of the pregnancy.
Do I keep gaining in the last month?
Usually yes, though the pace often slows in the final weeks and some women plateau or lose a pound or two just before labor. That is normal.
Why did I gain 4 pounds in one week?
Short-term jumps are usually fluid, not fat. One reading means little — but sudden swelling plus rapid gain is worth mentioning to your provider promptly.