Pregnancy Weight Gain Calculator
Free pregnancy weight gain calculator. See recommended IOM weight-gain ranges by pre-pregnancy BMI and your current week. No signup.
Recommended pregnancy weight gain by pre-pregnancy BMI
This calculator returns the total weight-gain range recommended by the Institute of Medicine (IOM) for your pre-pregnancy BMI, the weekly pace for the second and third trimesters, and an estimate of where you should sit at your current week. It is a guideline, not a personal target.
How the range and pace are found
Your pre-pregnancy BMI selects one of four bands. Each band carries a total range and a weekly rate for the second half of pregnancy:
| Pre-pregnancy BMI | Total gain | 2nd/3rd-trimester pace |
|---|---|---|
| Underweight (under 18.5) | 12.5 – 18 lb | 1 – 1.3 lb/week |
| Normal (18.5 – 24.9) | 11.5 – 16 lb | 0.8 – 1 lb/week |
| Overweight (25 – 29.9) | 7 – 11.5 lb | 0.5 – 0.7 lb/week |
| Obese (30 and above) | 5 – 9 lb | 0.4 – 0.6 lb/week |
The current-week estimate starts with a fixed 3 lb for the first trimester, then adds the weekly pace for weeks 14 through 27 and for every week past 27. It is a linear pace model, so it is most useful from the second trimester onward.
Worked example with the default inputs
The tool opens with a pre-pregnancy BMI of 22 and 16 weeks pregnant. A BMI of 22 falls in the normal band, with a total range of 11.5–16 lb and a pace of 0.8–1 lb per week.
- First-trimester allowance = 3 lb
- Weeks at pace = 16 − 13 = 3 weeks
- Low estimate = 3 + (3 × 0.8) = 5.4 lb, shown as 5 lb
- High estimate = 3 + (3 × 1.0) = 6 lb
At 30 weeks the same pace covers 17 weeks (14 in the second block plus 3 more), giving a range of about 17–20 lb. Because the model keeps adding the weekly pace after week 27, late-pregnancy estimates can approach or exceed the top of the total range; the total range remains the primary guideline.
Common mistakes
- Gaining to the full range in the first trimester. The first trimester usually adds only a few pounds; most gain happens after week 13.
- Using your current BMI. The band is set by the BMI you had before pregnancy, not the one you have now.
- Treating the range as a score. It is a healthy band, and gain is rarely linear; nausea can stall it early while the final weeks accelerate.
- Ignoring a twin pregnancy. Guidelines for multiples are higher and are set individually by a clinician.
When the numbers need medical input
These ranges apply to a singleton pregnancy and a healthy starting point. Twins, pre-existing conditions such as diabetes or high blood pressure, and a very high or very low pre-pregnancy BMI all change the appropriate target, which is why your provider sets your personal range. Use the calculator as context for that conversation, and track the direction of travel rather than any single weigh-in.
How much weight should I gain during pregnancy?
IOM guidance gives 12.5–18 lb for an underweight starting BMI, 11.5–16 for normal, 7–11.5 for overweight, and 5–9 for obese. Gaining within your band is linked to better outcomes for both mother and baby, but the band is wide and the trend across the pregnancy matters more than any one week.
Why is the first trimester only a few pounds?
The baby is still tiny, and the main early changes are blood volume and fluid. Many people lose a little in the first trimester because of nausea and food aversions, which is generally not a concern if it reverses once appetite returns.
Should I be worried if my gain is slightly above or below the range?
A single reading outside the band is common and not automatically a problem. Bring the pattern to your provider, who can look at the whole picture including the baby’s growth. Do not restrict food or aggressively diet during pregnancy without medical supervision.
Does the calculator change for twins?
It does not. The ranges shown are for a singleton pregnancy. Twin pregnancies have higher recommended gains, and because they carry additional risks, the target is set by your provider rather than by a general band.
This is an estimate, not medical advice. Your provider’s guidance takes precedence. Weight gain runs on the pregnancy timeline set by the pregnancy due date calculator, and the BMI calculator explains how the pre-pregnancy bands are defined. Calorie needs rise in later trimesters, which the TDEE calculator helps frame.