Clinical Calculators
Calculators and converters for daily clinical use — correct units, plain results.
Enter any value and all three update instantly. Conversion factor: 1 lb = 453.592 g · 1 oz = 28.3495 g.
In Aotearoa NZ, birthweight is assessed against customised centiles generated by the GROW (Gestation Related Optimal Weight) software, used as part of the national Aotearoa Growth Assessment Programme (GAP), commissioned by Te Whatu Ora. Customised centiles account for maternal height, pre-pregnancy weight, ethnicity, and parity — giving each pregnancy an individualised growth potential rather than applying a population average.
Key GROW centile thresholds:
<10th customised centile — Small for Gestational Age (SGA): triggers SGA/FGR surveillance pathway
10th–90th customised centile — Within expected growth potential
>90th customised centile — Large for Gestational Age (LGA): assess for macrosomia and gestational diabetes
Postnatal weight loss — Starship guidance:
Weight loss up to 7% of birth weight is expected in the first few days. Loss >7% warrants increased feeding review and monitoring. Loss ≥10% is a clinical threshold requiring assessment and may indicate need for supplementation or further investigation.
References: Aotearoa GAP, Perinatal Institute; Starship Clinical Guidelines — Weight loss in newborns.
Stones included for women who use or recognise this unit. Conversion: 1 stone = 14 lbs = 6.35029 kg.
Inches shown as whole numbers — clinical convention is "five foot seven", not "five foot six point nine". Conversion: 1 inch = 2.54 cm · 1 foot = 30.48 cm.
NZ Referral Guidelines thresholds: obstetric consultation at BMI ≥35 (32 weeks) · BMI ≥40 (14–16 weeks) · anaesthetic review at BMI ≥45 or BMI ≥40 with comorbidity · transfer of care at BMI ≥50.
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The NBS heel prick is performed after 24 hours of age. Collecting before 24 hours increases the risk of false positives and missed diagnoses. If the baby is discharged before the screen can be collected, arrange community midwife follow-up at the correct time.
Jaundice / hyperbilirubinaemia: Hour-specific thresholds apply — use the Bhutani nomogram or local phototherapy threshold chart (AAP/NICE). A bilirubin level that is acceptable at 24 hours may require treatment at 36 hours. Age in hours is required for accurate interpretation.
Vitamin K: IM dose given at birth. If oral regime — second dose at 3–5 days, third dose at 4 weeks. Timing documented from birth.
Discharge criteria: Many unit policies reference minimum age in hours (commonly ≥6 hours for vaginal birth, longer for operative). Document time of birth clearly for handover. References: NZ National Screening Unit — Newborn Metabolic Screening; Bhutani VK et al. (1999) Pediatrics 103(1):6–14.
Reference time defaults to now and updates on each page load and reset. Change it to calculate retrospectively — e.g. what was the baby's age at a specific observation time.
Day / Month / Year
Day / Month / Year · For IVF / assisted conception: use your fertilisation date, or subtract embryo age from transfer date — Day 5: transfer − 5 days · Day 3: transfer − 3 days.
Day / Month / Year
Enter a date above to see key milestones.
Naegele's rule: EDD = LMP + 280 days. Conception date: EDD = conception + 266 days (LMP = conception − 14 days). Enter gestation today in weeks+days to back-calculate all dates. Dating scan EDD takes precedence over LMP when discrepancy is >7 days (1st trimester) or >14 days (2nd trimester). Gestation shown as weeks+days (e.g. 28+3).