Pregnancy Weight Gain Calculator: How Much Should You Gain?
CodexFuse Team · 2026-11-04T03:25:33.686Z · 8 min read min read
Check your healthy pregnancy weight gain range by BMI and week with the free CodexFuse calculator, plus a worked example and weekly tracking plan.
A pregnancy weight gain calculator is a free online tool that estimates a healthy total weight gain range for pregnancy, based on pre-pregnancy body mass index (BMI) and the current week of pregnancy. Instead of guessing from a single chart, you enter your weight and week, and it returns a personalised range, your BMI category, and a weekly target to track against.
That matters because "eating for two" is misleading advice: most women need only a modest calorie increase, and the healthy range varies a lot by starting BMI.
What is a pregnancy weight gain calculator?
A pregnancy weight gain calculator estimates healthy pregnancy weight gain by combining your pre-pregnancy BMI with your current week. It returns a total gain range, your BMI category, and an approximate weekly target, so you can see whether your progress sits inside, above, or below the expected range.
The CodexFuse version keeps it simple: enter your weight, enter your week, press calculate. The tool is free to use as often as you like, and a weekly check takes under a minute.
How much weight should you gain in pregnancy?
There is no single correct number. The widely cited Institute of Medicine guidance sets different total ranges by pre-pregnancy BMI category, because starting underweight and starting with obesity carry different risks and needs. Find your category in the table below for your typical total range.
| Pre-pregnancy BMI | Category | Typical total gain range |
|---|---|---|
| Below 18.5 | Underweight | 12.5–18 kg |
| 18.5–24.9 | Normal weight | 11.5–16 kg |
| 25–29.9 | Overweight | 7–11.5 kg |
| 30 or above | Obesity | 5–9 kg |
Gain is uneven across pregnancy: often just 0.5–2 kg in the first trimester, with most gain in the second and third trimesters at roughly 0.4 kg per week for a normal-weight pregnancy. The trend across weeks is what counts, not a single weigh-in.
These ranges are general population guidance, not a personal prescription. Twin pregnancies, conditions such as diabetes or thyroid disorders, and severe nausea all change the picture — discuss a large gap with your clinician rather than correcting it alone.
How does the CodexFuse pregnancy weight gain calculator work?
The CodexFuse pregnancy weight gain calculator needs just two inputs — your weight and your current week — and returns your healthy gain range estimate, your BMI category, and your weekly target. The walkthrough below is verified against the live tool page.
- Enter your weight. Type in your current weight in the weight field.
- Enter your week. Type in your current week of pregnancy.
- Press calculate. The tool returns your healthy gain range estimate, your BMI category, and your weekly target.
Re-run it each week with your new weight and week. That comparison is the real value: it shows drift early, while small adjustments still work. If you are still pinning down dates, pair it with a due date calculator first, so the week you enter is accurate. A wrong week is the most common reason a result looks surprising.
Worked example: Sara's week-24 check
Meet Sara, a fictional example with real numbers. She is 1.65 m tall and weighed 62 kg before pregnancy. Her pre-pregnancy BMI is 62 ÷ (1.65 × 1.65) = 22.8 — normal weight — so her typical total range is 11.5–16 kg.
At week 24, Sara weighs 70 kg — a gain so far of 8 kg. She opens the pregnancy weight gain calculator, enters her weight and week 24, and gets a range of 11.5–16 kg with a weekly target of around 0.4 kg per week.
Reading the result: Sara has 3.5–8 kg left over roughly 16 weeks, or about 0.2–0.5 kg per week — comfortably inside her band. Her plan is simple: balanced meals, daily walks as her clinician advised, and a re-check at week 28 rather than daily weighing.
Consider the opposite case: had Sara gained 14 kg by week 24, she would already be near the top of her range with 16 weeks to go. That is not a reason to diet — dieting in pregnancy is unsafe without medical supervision — but it is a clear prompt to discuss portions, sugary drinks, and activity with her clinician.
Weigh yourself at the same time of day, on the same scale, once a week — not daily. Daily weight swings by a kilogram or more from water, meals, and clothing, and that noise hides the trend you actually need.
What if your weight gain is above or below the range?
If your gain is above or below the expected range, treat it as a signal to review, not a verdict. First confirm the trend over two to three weeks and check your inputs, then raise a persistent gap with your clinician, who can check for causes a calculator cannot see.
Common, fixable drivers of faster-than-expected gain include:
- Sugary drinks and snacks: juices and sweetened teas add calories without fullness.
- Portion creep: "eating for two" often doubles portions when only a small increase is needed.
- Less movement: nausea and fatigue quietly reduce daily activity.
- Fluid retention: later-pregnancy swelling adds scale weight that is not fat gain.
Run the free CodexFuse pregnancy weight gain calculator with your weight and week, and get your healthy range, BMI category, and weekly target in under a minute — fully managed, no subscription, no cost.
Get Started with CodexFuseHow to track your gain week by week
A result is only useful if you record it. The simplest routine that sticks:
| When | What to do | Why it helps |
|---|---|---|
| Weekly, same day | Weigh yourself once, same time and scale | Removes daily noise from the trend |
| After weighing | Run the calculator with your new weight and week | Updates your remaining range and weekly target |
| Monthly | Compare against your appointment weigh-ins | Catches scale or recording errors early |
| Each trimester | Review the total trend with your clinician | Turns numbers into a plan, not anxiety |
Keep a one-line note per week — date, week, weight, gain so far. After a month, that log gives your clinician concrete data instead of a vague "I think I've gained a lot."
For the dates side, the pregnancy calculator and ovulation calculator cover the dates side, while this calculator covers the weight side. After birth, the baby growth calculator continues the same tracking habit for your child.
New to pregnancy tracking? Start with the due date calculator guide to confirm your week, then return here to check your gain range.
What this calculator does not do
Honest limits matter with a health tool, so here they are plainly:
- It is not medical advice. The result is an estimate from general guidance and does not replace your clinician.
- It does not handle twins or multiples. Twin pregnancies have higher gain ranges, and this tool's ranges assume a singleton pregnancy.
- It cannot see body composition. Muscle, fluid, and fat weigh the same on a scale, so identical numbers can mean different things.
- It needs accurate inputs. A guessed pre-pregnancy weight or a wrong week produces a confident-looking but wrong range.
- It requires a free CodexFuse account. The tool is free and unlimited, but the tool page asks you to log in first.
Frequently Asked Questions
Is the pregnancy weight gain calculator free?
Yes. It is free and unlimited, though the tool page asks you to log in to a free account first. You can re-run it every week of your pregnancy at no cost.
What do I need to use the pregnancy weight gain calculator?
Just two inputs: your weight and your current week of pregnancy. The tool returns your healthy gain range estimate, your BMI category, and your weekly target.
How much weight should I gain in the first trimester?
Typically only around 0.5–2 kg in total, with most gain coming later. Many women gain little or lose slightly due to nausea, and that alone is not usually cause for alarm — discuss persistent loss with your clinician.
Can I use the calculator for a twin pregnancy?
Not reliably. Its ranges assume a singleton pregnancy, and twin pregnancies have higher recommended ranges. Use it only as a rough reference for multiples, and follow your clinician's guidance.
What should I do if I am gaining too fast?
First, confirm the trend over two to three weekly weigh-ins rather than reacting to one reading. Then review sugary drinks, portions, and activity, and raise it at your next appointment. Do not diet in pregnancy without medical supervision.
Does the calculator replace my doctor's advice?
No. It estimates a range from general guidance and your inputs, but cannot account for your medical history or scan findings. Your clinician's advice always takes priority.
Check your gain today, then keep tracking it
Pregnancy brings enough uncertainty without adding guesswork about weight. Open the pregnancy weight gain calculator now, enter your weight and week, and see exactly where you stand: your healthy range, your BMI category, and your weekly target, in under a minute.
Then make it a habit: weigh yourself once a week, re-run the calculator, and bring the log to your next appointment. If the trend drifts outside your range, you will catch it early — and walk in with real numbers to discuss. Move your pregnancy tracking to CodexFuse today: start with the free calculator, explore the matching due date and baby growth tools, and keep every check in one managed place, on credits, with no subscription in the way.
