A worked example: 3,200g at birth, 4,600g at 8 weeks
A baby born at 3,200g who now weighs 4,600g at 8 weeks old has gained 1,400g in total — an average of 175g per week, or 25g per day.
The formula: total gain ÷ age in weeks
Total gain = current weight − birth weight: 4,600g − 3,200g = 1,400g. Weekly average = total gain ÷ age in weeks: 1,400g ÷ 8 = 175g/week. Daily average simply divides the weekly figure by 7: 175 ÷ 7 = 25g/day.
A second example: 3,500g at birth, 5,900g at 12 weeks
A baby born heavier at 3,500g, now 5,900g at 12 weeks, has gained 2,400g total — a weekly average of 200g/week and a daily average of 28.6g/day, both higher than the first example.
Why this is an average, not a growth-chart assessment
This calculator reports the actual observed average rate over whatever period you enter — it doesn't classify the result against a percentile growth chart. As a general reference point, roughly 150-200g/week is typical in the first 3 months, tapering afterward, but individual healthy babies show a wide range, so a pediatrician plotting the trend against WHO growth standards is the real assessment, not this single average.