While I can't provide a crystal ball to reveal the future (que sera, sera), science provides a variety of ways to estimate how tall our children will be when they reach their adult height. The three methods described below use simple math and/or statistics to predict final stature, increasing in both complexity and accuracy from top to bottom.
Two Years Times Two
One of the most pervasive height estimation methods relies on doubling the height at age 2. While this old wives' tale method is not backed up by rigorous statistics, many pediatricians agree that it's not a bad predictor. "Doubling a child's height at age 2 can provide an estimate of how tall that child will be in adulthood. Boys are usually a little taller than that number and girls a little shorter" (Pittock, 2010). As this method tends to overestimate girls' final height, some physicians recommend doubling a girl's height at 18 months. This method provides a very rough estimate and has the downside of only being useful if baby is around 18-24 months old.
As adult height is largely a genetic trait, a variety of studies have shown that using parental height can provide a fairly accurate estimation, albeit with a large range. 90% of children with "parents of average stature" will end up within 7 inches of the calculated mid-parental height (Wright and Cheetham, 1999). Mid-parental height can be calculated by averaging the father's and mother's height and then adding 2.75 inches for boys or subtracting 2.75 inches for girls.
For example, if mom's height is 5'4" (64") and dad's height is 6'2" (74"), the mid-parental height would break down to:
Boys: (74+64)/2 + 2.75 = 71.75" or 5'11.75" (baby boy will likely grow to be 5'8"-6'3")
Girls: (74+64)/2 - 2.75 = 66.25" or 5'6.25" (baby girl will likely grow to be 5'3"-5'10")
If you don't feel like breaking out your calculator, check out this handy online calculator based on an older, but similar, mid-parental height equation from Tanner et al., 1970. While the mid-parental height equation provides a useful estimate for a couple's future and current offspring, the 7 inch margin of error definitely leaves room for improvement. Additionally, this equation is recommended only for parents of average height. "Where parents were unusually tall or short, their children were relatively less tall or short, respectively, and the mid-parental height was a poor predictor of attained height" (Wright and Cheetham, 1999).
Statistics-Based Growth Chart
In 2011, researchers set out to "develop a chart to predict a child's adult height from their current height" by crunching longitudinal data (Cole and Wright, 2011). They discovered that height at certain ages is more predictive than others, with height before 2 years old and height during puberty the least helpful for predicting adult height. The growth chart generated by this study for children age 2-4 years old is provided below (Cole and Wright, 2011) with a few additions in red for clarity.
How to use the chart:
If your child is between 3.5-4 years old: plot their age in months (x-axis) vs. height in cm (y-axis) to find their percentile (blue or pink line). For children outside of this range, find their percentile using an online tool by entering age and height.
Find the blue or pink percentile line in the "Adult Height Prediction" bar and read off the adult height in either feet/inches or centimeters.
For 4 out of 5 children, the predicted height will be within ± 6 cm (2.36 inches) of the true value. (Calculations for kids outside of the 2-4 year range are possible. Comment below if you are interested in a breakdown of the math.)
That's the long and the short of it! If you're curious about how big your little one might grow up to be, try out these methods to predict their adult height.
Pittock, Siobhan. "Child's Height at Age 2 May Predict Adult Height.” Mayo Clinic, Mayo Foundation for Medical Education and Research, 10 Sept. 2010, newsnetwork.mayoclinic.org/discussion/childs-height-at-age-2-may-predict-adult-height/.
Wright CM, Cheetham TD. The strengths and limitations of parental heights as a predictor of attained height. Arch Dis Child. 1999 Sep;81(3):257-60. doi: 10.1136/adc.81.3.257. PMID: 10451401; PMCID: PMC1718044.
Tanner JM, Goldstein H, Whitehouse RH. Standards for children's height at ages 2-9 years allowing for heights of parents. Arch Dis Child. 1970 Dec;45(244):755-62.
Cole TJ, Wright CM. A chart to predict adult height from a child's current height. Ann Hum Biol. 2011 Nov;38(6):662-8.