Pregnancy Weight Gain Calculator
Recommended pregnancy weight gain by pre-pregnancy BMI and week, using the Institute of Medicine 2009 ranges, with twins handled and a week-by-week target table.
Pregnancy Weight Gain Calculator: with the default inputs, where you are against the guideline is Within the guideline range for this week.
Gestational age in completed weeks, counted from the first day of your last period.
- Weight gained so far
- 15 lb
- Recommended by now, from
- 9.9 lb
- Recommended by now, to
- 15.4 lb
- Recommended total gain, from
- 25 lb
- Recommended total gain, to
- 35 lb
- Pre-pregnancy BMI
- 23.3
- Pre-pregnancy BMI category
- Normal weight
- Recommended gain per week from here
- 0.8–1 lb per week (0.36–0.45 kg)
Assumptions
- Ranges are the Institute of Medicine / National Research Council 2009 guidelines, which use the WHO BMI cut-offs applied to pre-pregnancy weight.
- The first-trimester figure of 1.1–4.4 lb (0.5–2 kg) is an assumption the IOM states in a footnote when calculating its weekly rates, not a recommendation. It is shown here as a smooth ramp to week 13 for readability.
- Kilogram figures are converted from the published pound ranges. The IOM's own kilogram ranges are rounded slightly differently (for example 17–25 kg rather than 16.8–24.5 kg for normal-weight twins).
- Twin figures are the IOM's provisional guidelines and give a total only. The week-by-week twin band is this calculator's linear interpolation to 37 weeks, not an IOM recommendation, and no recommendation exists for underweight women carrying twins.
- Pre-pregnancy BMI is calculated from the weight and height you enter; recalled pre-pregnancy weight is often a little low.
- This is a guideline reference, not medical advice and not a diagnosis. Your midwife or obstetrician's plan takes precedence.
| Week | From(lb) | To(lb) | Mid-point(lb) |
|---|---|---|---|
| 0 | 0 lb | 0 lb | 0 lb |
| 1 | 0.1 lb | 0.3 lb | 0.2 lb |
| 2 | 0.2 lb | 0.7 lb | 0.4 lb |
| 3 | 0.3 lb | 1 lb | 0.6 lb |
| 4 | 0.3 lb | 1.4 lb | 0.8 lb |
| 5 | 0.4 lb | 1.7 lb | 1.1 lb |
| 6 | 0.5 lb | 2 lb | 1.3 lb |
| 7 | 0.6 lb | 2.4 lb | 1.5 lb |
| 8 | 0.7 lb | 2.7 lb | 1.7 lb |
| 9 | 0.8 lb | 3 lb | 1.9 lb |
| 10 | 0.8 lb | 3.4 lb | 2.1 lb |
| 11 | 0.9 lb | 3.7 lb | 2.3 lb |
| 12 | 1 lb | 4.1 lb | 2.5 lb |
| 13 | 1.1 lb | 4.4 lb | 2.8 lb |
Cumulative gain since your pre-pregnancy weight. The first thirteen weeks are shown as a ramp toward the 1.1–4.4 lb first-trimester figure, which the IOM states as a calculation assumption in a footnote rather than as a recommendation.
| Pre-pregnancy BMI | Total gain, singleton | Rate, 2nd/3rd trimester | Total gain, twins |
|---|---|---|---|
| Underweight (under 18.5) | 28–40 lb (12.7–18.1 kg) | 1–1.3 lb/week | No recommendation — insufficient data |
| Normal weight (18.5–24.9) | 25–35 lb (11.3–15.9 kg) | 0.8–1 lb/week | 37–54 lb (16.8–24.5 kg) |
| Overweight (25.0–29.9) | 15–25 lb (6.8–11.3 kg) | 0.5–0.7 lb/week | 31–50 lb (14.1–22.7 kg) |
| Obesity (30 and above) | 11–20 lb (5–9.1 kg) | 0.4–0.6 lb/week | 25–42 lb (11.3–19.1 kg) |
Institute of Medicine and National Research Council, Weight Gain During Pregnancy: Reexamining the Guidelines (2009). Twin figures are the report's provisional guidelines.
How this is worked out
The formula
Pre-pregnancy BMI = pre-pregnancy weight (kg) ÷ height (m)² Recommended cumulative gain by week w (singleton): w ≤ 13: ramp toward 1.1–4.4 lb across the first trimester w > 13: 1.1–4.4 lb + (weekly rate for your BMI category) × (w − 13) Weekly rates (2nd/3rd trimester, lb/week): Underweight 1.0–1.3 · Normal 0.8–1.0 · Overweight 0.5–0.7 · Obesity 0.4–0.6
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Pre-pregnancy weight
- A number.in lb, kg, st · from 30 to 600 · defaults to 140
- Height
- A number.in ft, in, cm, m · from 3 to 8.5 · defaults to 5.4167
- Current weight
- A number.in lb, kg, st · from 30 to 600 · defaults to 155
- Weeks pregnant
- Gestational age in completed weeks, counted from the first day of your last period.from 1 to 45 · whole numbers only · defaults to 24
- Number of babies
- Choose one of 2 options.One (singleton) · Twins
What you get back
- Where you are against the guidelinemain answer
- Weight gained so far
- Recommended by now, from
- Recommended by now, to
- Recommended total gain, from
- Recommended total gain, to
- Pre-pregnancy BMI
- Pre-pregnancy BMI category
- Recommended gain per week from here
What this assumes
- Ranges are the Institute of Medicine / National Research Council 2009 guidelines, which use the WHO BMI cut-offs applied to pre-pregnancy weight.
- The first-trimester figure of 1.1–4.4 lb (0.5–2 kg) is an assumption the IOM states in a footnote when calculating its weekly rates, not a recommendation. It is shown here as a smooth ramp to week 13 for readability.
- Kilogram figures are converted from the published pound ranges. The IOM's own kilogram ranges are rounded slightly differently (for example 17–25 kg rather than 16.8–24.5 kg for normal-weight twins).
- Twin figures are the IOM's provisional guidelines and give a total only. The week-by-week twin band is this calculator's linear interpolation to 37 weeks, not an IOM recommendation, and no recommendation exists for underweight women carrying twins.
- Pre-pregnancy BMI is calculated from the weight and height you enter; recalled pre-pregnancy weight is often a little low.
- This is a guideline reference, not medical advice and not a diagnosis. Your midwife or obstetrician's plan takes precedence.
About this calculator
How much weight you should gain in pregnancy depends almost entirely on one thing: what you weighed before. The Institute of Medicine's 2009 guidelines set four ranges by pre-pregnancy BMI, and they are the standard used across US obstetric care. This calculator applies them to your week and shows whether you are inside the band, along with the whole trajectory.
The ranges
For a single baby, the IOM recommends:
- Underweight (BMI under 18.5): 28–40 lb (12.5–18 kg), gaining 1.0–1.3 lb a week in the second and third trimesters
- Normal weight (18.5–24.9): 25–35 lb (11.5–16 kg), 0.8–1.0 lb a week
- Overweight (25.0–29.9): 15–25 lb (7–11.5 kg), 0.5–0.7 lb a week
- Obesity (30 and above): 11–20 lb (5–9 kg), 0.4–0.6 lb a week
The first trimester is handled separately, and carefully: the IOM does not recommend a first-trimester figure. Its weekly rates are calculated on the assumption of a 1.1–4.4 lb (0.5–2 kg) gain across all thirteen weeks, stated in a footnote. Many people gain nothing at all in that period, or lose a little to nausea, and that is normal.
Twins
The IOM published provisional twin guidelines, and they are provisional for a reason — the evidence base is much thinner. Normal weight: 37–54 lb. Overweight: 31–50 lb. Obesity: 25–42 lb. For underweight women carrying twins the IOM gives no recommendation at all, saying there was insufficient data to set one. This calculator says so plainly rather than inventing a number.
The twin guidance is also a total only, with no weekly rate. The week-by-week band shown for twins spreads that total between the end of the first trimester and 37 weeks, which is this calculator's interpolation and not something the IOM published.
How to use the result
Compare where you are with the band for your week, then take the answer to your next appointment rather than acting on it. A single weigh-in tells you very little — scales move with fluid, time of day, clothing and the bowel, and pregnancy adds swelling on top. The trend across several appointments is what your provider is watching.
Two things worth saying plainly
Gaining below the range is not the safe side. Insufficient gestational weight gain is associated with low birth weight, small-for-gestational-age babies and preterm birth. Pregnancy is not a time to run a calorie deficit, and no one should be dieting to stay inside the lower end of a band on a web page.
Gaining above the range is common and is not a moral failure. More than half of pregnancies in the US exceed the IOM range. It is associated with higher risks of gestational diabetes, caesarean delivery and retained weight afterwards, which is worth discussing — through food quality, activity and support, not restriction.
If a number on this page makes you want to eat less, that is the signal to talk to your midwife or doctor about it instead.
Frequently asked questions
▸How much weight should I gain in pregnancy?
It depends on your pre-pregnancy BMI: 25–35 lb if you started at a normal weight, 28–40 lb if underweight, 15–25 lb if overweight, and 11–20 lb with obesity. Those are the Institute of Medicine's 2009 ranges.
▸How much should I gain in the first trimester?
The IOM assumes 1.1–4.4 lb (0.5–2 kg) across the whole first thirteen weeks when it calculates its weekly rates — it does not set that as a recommendation. Gaining nothing, or losing a little to nausea, is common and usually fine.
▸What if I am gaining too fast?
Raise it at your next appointment. The answer is almost never a calorie deficit — it is usually about food quality, drinks, and whether activity is still possible. Restricting intake in pregnancy carries its own risks.
▸What if I am not gaining enough?
Tell your provider sooner rather than later. Low gestational weight gain is linked to low birth weight and preterm birth, and it can also be a sign that nausea or food access is a bigger problem than it looks.
▸What about twins?
The IOM's provisional twin ranges are 37–54 lb for normal weight, 31–50 lb for overweight and 25–42 lb with obesity. There is no recommendation for underweight women with twins, because the evidence was not there to set one.
Put this calculator on your own site
A working pregnancy weight gain, free for any site, with no ads and no sign-up. It resizes to fit wherever you paste it and updates itself as this page improves.
Paste this anywhere. It works on any site, carries no ads, never expires, and always shows the current version.
Pregnancy Weight Gain Calculator by CalculateItNow
The page's own title. The clearest description of what the link leads to.
The credit line sits outside the widget on purpose, so it is a real link on your page rather than one buried in a frame. Please keep it — it is what pays for CalculateItNow staying free and ad-free. The script only resizes the widget to fit its contents; drop it and the widget still works.
Browse every calculator widget·How to add it to WordPress, Squarespace or Wix
Related calculators
The questions people ask next to a pregnancy weight gain.
Due date from your last period, conception date, IVF transfer or a scan date, with how many weeks pregnant you are today, trimester and key milestone dates.
Calculate your body mass index from height and weight, see your category, and find the weight range that counts as healthy for your height.
Work backwards to the estimated conception date from a due date, a last period or a birth date, with the fertile window that produced it and an honest error range.
Predict your next several periods and fertile windows from your last period and cycle length, with the day of your cycle today and what counts as normal variation.
Find how many calories a day to eat to maintain, lose or gain weight, with BMR and TDEE shown, Mifflin-St Jeor by default, and warnings if the target is too low.