Pregnancy Weight Gain Calculator — Plan Healthy Gain for You & Baby

You’re pregnant and want to know how much weight is healthy for you and your baby. Great — that’s exactly what this tool helps with. Enter your pre-pregnancy weight, height, and which trimester you’re in. Optionally add your current weight to see how you’re tracking. The calculator tells you:

• Your pre-pregnancy BMI and BMI category
  
• The recommended total weight gain range for your pregnancy (based on your BMI)
  
• A recommended weekly gain rate for the 2nd and 3rd trimesters
  
• If you entered current weight: how much you’ve gained so far and how much remains
  

Everything below explains the reasoning, the formulas, and how to use the calculator safely.

Why this matters

Healthy weight gain supports baby growth and reduces risks for both mother and child. Too little gain can increase the risk of low birth weight; too much gain increases risk for gestational diabetes, high blood pressure, difficult delivery, and postpartum weight retention. Using evidence-based targets (the Institute of Medicine / National Academies guidance) helps keep pregnancy on a healthy track.

The guidelines we use (short version)

Recommendations below follow widely accepted IOM (Institute of Medicine) ranges for a singleton pregnancy:

• Underweight (BMI < 18.5): 12.5–18 kg (28–40 lb) total
  
• Normal weight (BMI 18.5–24.9): 11.5–16 kg (25–35 lb) total
  
• Overweight (BMI 25.0–29.9): 7–11.5 kg (15–25 lb) total
  
• Obese (BMI ≥ 30.0): 5–9 kg (11–20 lb) total
  

(If you’re pregnant with twins or have other medical conditions, recommendations differ — see your clinician.)

Key formulas & rates used by the calculator

1. Body Mass Index (BMI):
   

BMI = weight (kg) ÷ [height (m)]²

Example: 65 kg, 165 cm → height = 1.65 m → BMI = 65 / (1.65²) ≈ 23.9

2. Total recommended gain: Choose the IOM range that matches your BMI category (see table above).
   
3. Typical pattern of gain by trimester:
   

• First trimester (0–13 weeks): small total gain — about 0.5–2.0 kg (1–4 lb) total for most people.
  
• Second & third trimesters (weeks 14–40): steady weekly gain:
  
  • Underweight: ≈ 0.45–0.59 kg/week (≈1.0–1.3 lb/wk)
    
  • Normal weight: ≈ 0.36–0.45 kg/week (≈0.8–1.0 lb/wk)
    
  • Overweight: ≈ 0.23–0.32 kg/week (≈0.5–0.7 lb/wk)
    
  • Obese: ≈ 0.17–0.27 kg/week (≈0.4–0.6 lb/wk)
    

(These weekly rates are averages used to split the remaining recommended gain after the first trimester.)

4. If you enter Current Weight:
   

• Gain so far = Current Weight − Pre-pregnancy Weight
  
• Remaining recommended gain = Recommended total (midpoint or range) − Gain so far
  

How the calculator works

1. You enter Pre-pregnancy Weight (kg) and Height (cm). (If you prefer pounds/inches, convert or choose alternate units.)
   
2. The calculator computes your BMI and places you in a BMI category (underweight, normal, overweight, obese).
   
3. Based on that category it displays the recommended total weight-gain range (kg and lb).
   
4. You select your Trimester (1st / 2nd / 3rd). The tool shows typical expected gain up to this point (first trimester small total; second/third use weekly rates).
   
5. Optional: enter your Current Weight. The calculator then:
   
   • shows your actual gain so far,
     
   • compares it to the expected/typical gain for your trimester, and
     
   • shows how much remains to reach the IOM recommended range (and suggested weekly gain going forward).
     
6. The tool gives a simple plan and gentle flags if you’re well above or below the recommended track, with a reminder to discuss with your healthcare professional.
   

Practical example

• Pre-pregnancy weight: 68 kg; height: 165 cm → BMI ≈ 25.0 → Overweight category.
  
• Recommended total gain: 7–11.5 kg.
  
• If currently trimester 2 and current weight is 72 kg: gain so far = 4 kg. Remaining recommended (midpoint ~9.25 kg) ≈ 5.25 kg to reach midpoint; but the calculator will show the full range left (3–7.5 kg depending on your target).
  

FAQs