How we calculate
Every number on this site comes from a public health guideline or a standard medical formula. Here they are.
| Tool | Method and source |
|---|---|
| Due date | Naegele's rule: last period + 280 days, adjusted for cycle length. Conception + 266 days. IVF: day-5 transfer + 261 days, day-3 transfer + 263 days. |
| How far along | Days since (due date − 280 days). Trimesters: weeks 0–13, 14–27, 28 onward (ACOG). |
| Baby size by week | Rounded averages from published fetal growth tables. Crown-to-rump length until week 19, head-to-heel from week 20. |
| Caffeine | 200 mg a day in pregnancy (ACOG, NHS). Up to 300 mg a day while breastfeeding (CDC). Drink values are typical NHS amounts. |
| Breast milk storage | CDC breast milk storage guidelines for healthy, full-term babies. |
| Ovulation | Calendar method: ovulation about 14 days before the next period. Fertile window = 5 days before ovulation + ovulation day. |
| Adjusted age | Real age − weeks born early, measured from the original due date (American Academy of Pediatrics). |
| Baby teeth | American Dental Association tooth eruption chart. |
Important
These tools give estimates for most people. They are not medical advice and can't replace your doctor or midwife. If a result worries you, or if you feel unwell, contact a health professional. In an emergency, call your local emergency number.