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.
How to Use This Calculator
1. Enter the LMP date
Use the labelled fields and units that match your situation.
2. Calculate instantly
The result, visual comparison, and working update as values change.
3. Discuss the estimate with your clinician
Check assumptions, then copy, print, or share the calculation.
Practical Examples & Use Cases
| Starting date | Method | Calculation | Planning use |
|---|---|---|---|
| 1 Jan | LMP | +280 days | Estimated due date |
| Known clinical date | Ultrasound | Clinician dating | Confirm or revise estimate |
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
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.
Related Calculators & Tools
IVF Pregnancy Calculator
Week 21 guidance and calculation for this pregnancy timeline.
Twin Pregnancy Calculator
Week 21 guidance and calculation for this pregnancy timeline.
Pregnancy Countdown Calculator
Week 21 guidance and calculation for this pregnancy timeline.
Conception Calculator
Week 21 guidance and calculation for this pregnancy timeline.
Pregnancy Calculator — Week 20
Review the previous week in this pregnancy timeline.
Pregnancy Calculator — Week 22
Continue to the next week in this pregnancy timeline.