Growth Velocity Calculator

Choose two dated records for the same person and enter the earlier one first. Use the original dates, even for older records. The second date must be later; same-day readings do not give an elapsed interval for calculating a rate.

Choose cm or inches and fill in both heights, up to the equivalent of 300 cm. Use measurements taken in the same way. Calculate, then read the actual change and elapsed days before the yearly and monthly equivalents.

After editing a date, height or unit, calculate again to see an updated result. Reset example loads 130 cm on January 1, 2025 and 133 cm on July 1, 2025: a 181-day interval. The 2024 example below includes a leap day and lasts 182 days.

• Use original dates rather than treating every month as 30 days.
• In inch mode, enter total inches rather than a feet-and-inches combination. One inch equals exactly 2.54 cm.
• Switching units converts both entered heights together. Results always use cm, cm/year and cm/month.

First subtract the earlier height from the later height. This is the actual recorded height change, which can be positive, zero or negative. Next divide that change by the number of calendar days between the measurements, then multiply by 365.25 to express the same average rate per year.

Elapsed days are the difference between the dates, without counting both endpoints as an extra full day. January 1 to January 2 is one day. Leap days are included, and daylight-saving changes do not change the calendar-day count. Annualization always uses 365.25, rather than selecting 365 or 366 according to the starting year.

The monthly equivalent is the annualized rate divided by 12. It describes the same interval using an average month, not an observed calendar month or an expected future gain. Results are rounded to at most two decimal places.

Suppose height was 130 cm on January 1, 2024 and 133 cm on July 1, 2024. That interval contains 182 days, including February 29. The recorded change is 3 cm; its annualized equivalent is 3 ÷ 182 × 365.25, or about 6.02 cm/year.

Divide 6.020604… by 12 to get about 0.50 cm/month. The measured change is still 3 cm. Yearly and monthly figures express that same interval’s average rate; they are not additional growth to add to the total.

The table places the same 3 cm change in different dated intervals. A shorter interval produces a higher annualized rate; the last row is the page's reset example. Even when annualized figures are similar, future growth can vary with age, puberty, season and individual circumstances.

Measure on a level floor against a vertical wall or with a stadiometer. Remove shoes and bulky hair accessories, keep the feet flat, stand upright and look straight ahead. Use a flat headpiece at a right angle to the wall and read the scale carefully.

Use the same equipment, posture and measurement technique each time. A similar time of day helps when tracking small changes. Skirting boards, carpet, a tilted book, hair and shoe soles can affect a reading. Note equipment changes, such as moving from a wall measurement at home to a clinic's stadiometer.

Do not compare a baby's recumbent length directly with a child's standing height: changing the method can create a difference unrelated to growth. If the method must change, keep that context in the record so later interpretation can account for the different conditions instead of relying on the numerical gap alone.

• Keep the original measurement dates rather than estimating the number of months.
• Repeat a doubtful reading with the same posture, without selecting the most appealing result.
• Record footwear, time of day and the equipment used.
• Record only the precision your equipment supports. Unit conversion cannot recover precision that was never measured.

A small measurement error becomes a much larger apparent yearly change when the interval is short. For example, a 0.5 cm difference over 30 days annualizes to about 6.09 cm/year, even if much of that difference came from posture or measurement variation. This tool therefore shows the actual change and elapsed days beside the rate.

The table isolates one example: 0.5 cm of measurement error in the height difference. It shows how that error affects the yearly rate at different intervals. It does not set a maximum error or recommend when to measure; real error depends on equipment and technique.

Frequent measurements help only when the method is consistent. Daily readings may mainly show noise. Choose a repeat interval suited to age and purpose, with professional guidance where needed, rather than selecting the pair that gives the highest rate.

Identical entered heights produce zero recorded change and zero annualized growth. This means that no difference is visible at the precision of those records, rather than proving that no growth occurred anywhere within the interval. For example, records rounded to whole centimetres may hide a small change.

A negative value means the later entered height is lower. Check the date order, cm versus inches, posture, footwear, equipment and time of day. If 133 cm becomes 132.5 cm over 60 days, the recorded difference is −0.5 cm and the annualized rate is about −3.04 cm/year. That annualized figure cannot explain the cause.

Do not swap the heights simply to remove a negative sign: each measurement must stay attached to its correct date. Repeat measurements under consistent conditions first. If reliable repeated measurements continue to decline, or other concerns are present, take the complete record to a qualified professional. This page does not classify a zero or negative result as a disease.

Keep the original date, height, unit and measuring conditions, not just the annualized result. You can optionally enable browser measurement history and select two saved readings for the same person and method on different dates. The tool puts them in date order for calculation.

With three or more measurements, you can enter consecutive pairs or compare the first and last records over a longer span. Consecutive intervals help reveal changes in the rate, while the first-to-last interval summarizes a longer average. A long interval can also hide variation in between, so these views serve different purposes.

This page compares two entries at a time. You can save the later measurement to optional local history, or use a shared measurement from another tool and add the second reading. Local history keeps dates, heights and measuring methods in this browser, not a cloud account or an automatic trend analysis. Clearing browser data removes the records; keep a separate copy if needed.

• Keep original dates and readings before calculating interval rates.
• Compare interval lengths alongside rates so measurement noise is not mistaken for sudden acceleration.
• Adjacent intervals sharing an endpoint are affected by the same measurement error and are not completely independent evidence.

A height percentile places one measurement in a reference distribution for a particular age and reference sex. Growth velocity instead describes the change between two dates. Neither is a substitute for the other, and a height percentile chart is not itself a reference for growth velocity.

The same 6 cm/year can mean different things at different ages and stages of puberty. Infants, children, adolescents and adults cannot share one normal threshold. This calculator does not collect age, reference sex or pubertal stage, so it calculates change without classifying it as normal or abnormal for an age group.

You can separately use the children's height percentile tool to explore individual measurements, keeping the dates in your own record. A high percentile does not guarantee fast current growth, and a low percentile does not necessarily mean slow growth. Clinical interpretation also considers family heights, development, symptoms, measurement quality and past records. Two readings cannot establish remaining growth or adult height.