Pregnancy Calculator — Week 21: Baby Size, Symptoms & Due Date
You are in week 21 of a standard singleton pregnancy. Below is a complete evidence-based snapshot — baby's growth, your body, nutrition, exercise, red flags and a doctor visit checklist for this exact week.
Pregnancy Calculator
Enter the first day of your last menstrual period (LMP). EDD = LMP + 280 days.
Baby at week 21
This week: Rapid brain growth. Digestive system produces meconium. Fetus responds to sound with movement.
Mother's body — what changes
In week 21 you may notice: Varicose veins may appear. Heartburn common as uterus pushes stomach up.
Nutrition & supplements
Add ~340 kcal/day above pre-pregnancy baseline. Prioritise iron (27 mg/day), calcium (1000 mg), omega-3 DHA (200–300 mg) and 71 g protein. Continue prenatal vitamin.
Safe exercise
Continue 150 min/week. Avoid supine (flat-on-back) exercises after week 20 — they compress the vena cava. Swimming and prenatal Pilates are ideal now.
Doctor visit checklist — week 21
- ✓Start iron supplement if hemoglobin <11 g/dL
- ✓Blood pressure + weight + urine dipstick at every visit
- ✓Fetal heart tones from week 10–12 (Doppler)
Warning signs — call your provider immediately
- ⚠Heavy bleeding (soaking a pad in an hour)
- ⚠Severe abdominal pain that does not ease
- ⚠Fever above 38°C / 100.4°F
- ⚠Sudden gush of fluid (early rupture of membranes)
- ⚠Absent fetal movement for 12+ hours after 24 weeks
- ⚠Severe headache + visual disturbance (preeclampsia)
Week 21 — Frequently asked questions
How accurate is the Pregnancy Calculator at week 21?
The calculator uses standard gestational-age arithmetic (LMP + 280 days for standard; egg retrieval + 266 days for IVF day-5). Ultrasound crown-rump length between weeks 8–13 is more accurate (±5 days) than LMP — adjust EDD accordingly if the scan differs by more than 7 days.
What size is my baby at week 21?
Approximately the size of a carrot — length 26.7 cm and weight 360 g. These are median values from ACOG, NHS UK and Mayo Clinic references.
Which symptoms are normal in week 21?
Varicose veins may appear. Heartburn common as uterus pushes stomach up. Every pregnancy is different — call your provider if anything on the warning-signs list appears.
Should I have an ultrasound at week 21?
Start iron supplement if hemoglobin <11 g/dL. Routine scan windows are: dating (10–13w), anatomy (18–22w), growth (28–32w).
How much weight should I gain by week 21?
Approximately 5.5 kg cumulative if you started at a normal BMI (IOM guideline). Underweight mothers gain more; overweight mothers less.
What is my EDD if today is week 21?
Your estimated due date is 19 weeks from today. Calculator adds (280 − 7 × 21) days to today's date.
Can I travel during week 21?
Second trimester (weeks 14–27) is the safest travel window. Wear compression stockings for flights over 4 hours.
Content aligned with ACOG, NHS UK and Mayo Clinic. Reviewed by Dr. Maria Rehman, MD (OB/GYN). This page is educational and does not replace personal medical advice — call your obstetrician for any concern.