Conception Calculator — Week 15 From Conception (Fetal Age)
You are 15 weeks from conception, which corresponds to 17 weeks of gestational age (LMP-based). This page focuses on true fetal age — how long the baby has actually been developing since fertilisation.
Conception Calculator
Enter your LMP. Fetal age = gestational age − 2 weeks.
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 15
At 15 weeks from conception (17w gestational): Bones harden. Fetus can sense light through closed eyelids. Practices breathing amniotic fluid.
Mother's body — what changes
15 weeks post-conception, your body is: Nasal congestion. Gums may bleed when brushing (pregnancy gingivitis). Bump becomes noticeable.
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. Week 15 from conception (17 weeks gestational) needs targeted micronutrients — the developmental window differs from LMP-based advice.
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. At 15 weeks from conception, low-impact activity supports placental blood flow without stressing the fresh implantation.
Doctor visit checklist — week 15
- ✓Book anatomy scan for 18–22 weeks
- ✓Note: 15 weeks from conception = 17 weeks LMP — clinic dating uses LMP
- ✓Confirm dating with crown-rump length at 8–13 weeks (±5 days accuracy)
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 15 — Frequently asked questions
Content aligned with ACOG dating criteria and Mayo Clinic conception timeline. 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
Pregnancy Calculator
Week 15 guidance and calculation for this pregnancy timeline.
IVF Pregnancy Calculator
Week 15 guidance and calculation for this pregnancy timeline.
Twin Pregnancy Calculator
Week 15 guidance and calculation for this pregnancy timeline.
Pregnancy Countdown Calculator
Week 15 guidance and calculation for this pregnancy timeline.
Conception Calculator — Week 14
Review the previous week in this pregnancy timeline.
Conception Calculator — Week 16
Continue to the next week in this pregnancy timeline.