How to compare InBody scans over time

Start with the record, before interpreting the change

Put the two original reports side by side. Confirm that they belong to the same person, then check the test date, device and unit beside each value. Copy the current result from each sheet rather than a reference range, a target or a number from the sheet’s history graph. Keep the original report available when reviewing your transcription.

A useful comparison begins with a small set of clearly named fields. InBody’s terminology distinguishes skeletal muscle mass from fat-free mass: skeletal muscle is a component of the body, while fat-free mass includes all components that are not fat.^[1] Do not rename both as “muscle” in a spreadsheet or compare one with the other.

Worked example: calculate what the reports say

The following numbers are invented for an arithmetic example. They are not real scans, a transformation story or expected results from a training program. Both records use kilograms and matching field labels. Download the example CSV for the two rows in a spreadsheet-friendly format.

For each mass field, subtract the first value from the second. Skeletal muscle mass is 35.2 − 35.0 = +0.2 kg. Describe that as “the reported skeletal muscle mass was 0.2 kg higher.” That wording keeps the observation separate from an explanation of why it happened.

Percent body fat needs careful wording. Moving from 20.0% to 19.0% is a decrease of one percentage point. Relative to the original 20.0%, it is a 5% decrease: (19 − 20) ÷ 20 × 100 = −5%. Those are two ways to describe the same displayed percentage change, not a statement that someone lost 5% of their body weight.

The example also shows why rounded values can differ slightly from a fresh calculation. At the second date, 15.0 ÷ 79.0 × 100 is approximately 18.99%, which rounds to 19.0%. Preserve the source precision rather than adding decimal places that the report never supplied. If you calculate another field yourself, label it as calculated.

Check whether the testing conditions are comparable

InBody’s official guidance asks for consistent conditions between tests and identifies factors including hydration, nutrition and recent intensive exercise as relevant to results.^[2] Follow the current instructions for your device and testing facility. The purpose of a condition note is to help recognize a changed setup, not to create your own testing protocol.

• Was the device model and testing location the same? If you do not know the model, write “not recorded.”
• Were the test time and preparation comparable according to the facility’s instructions?
• Does either record have a known difference, such as testing after exercise when the earlier visit was before it?
• Did the operator or report identify a problem with the measurement? Preserve that note with the result.

Use specific notes, such as “different device” or “time not recorded,” instead of retrospectively marking every visit “same conditions.” A missing detail is not proof that the conditions matched. When you cannot establish comparability, you can still keep both reports without presenting their difference as a precise tissue change.

Repeatability and accuracy answer different questions

In a 2024 study, Looney and colleagues measured 14 healthy military-age adults with an InBody 770 on five controlled visits, taking duplicate measurements. Results were highly repeatable under those conditions. However, comparison with DXA showed systematic differences: InBody reported lower body fat percentage and fat mass, and higher fat-free mass in this sample.^[3]

Repeatability asks whether repeated measurements agree with one another. Agreement with another method is a separate question. This small, controlled study does not establish that every small change in an individual’s report represents tissue gained or lost. Its average differences are not a correction formula to apply to your own scans.^[3]

Review a photo before saving its numbers

Photograph the whole sheet clearly enough to read its headings and decimal points. During transcription or scan review, check each value against its label. A chart can place a mass, a percentage and a reference marker close together; selecting the wrong number can produce a plausible-looking entry in the wrong field.

Use the date of the test rather than the day you photographed it. Confirm the unit instead of assuming kilograms, and check that 35.2 has not become 352. Leave unavailable optional fields blank. If an essential value is unreadable, return to the source or enter a clearer record rather than replacing it with zero.

Keep calculated metrics distinct from reported ones

Using the example’s rounded mass values, calculated fat-free mass is 80 − 16 = 64 kg at the first date and 79 − 15 = 64 kg at the second. Neither equals the skeletal muscle mass entry. Giving the spreadsheet columns their full names prevents the apparent contradiction of “muscle stayed the same” in one column and “muscle increased” in another.

The FFMI calculator uses body weight, fat mass and height to calculate fat-free mass index. Enter weight and fat mass in kilograms, and height in centimetres. It is another calculation from the information you enter, not an independent body-composition measurement. Keep the same inputs and calculation method when reviewing its history, and retain the original reported values alongside it.

What belongs in a useful comparison note?

A clear note separates three things: the recorded difference, the known conditions and the remaining uncertainty. For this example: “Reported skeletal muscle mass +0.2 kg; same device label in both records; this difference alone does not establish tissue gain.” Avoid assigning a cause such as a particular workout or supplement when the records do not establish one.

Keep training results in their own record too. The workout log template captures completed sets, while estimated 1RM, volume and rep PRs explains what those summaries mean. A set record and a body-composition report answer different questions; storing both clearly is more useful than forcing them into one verdict.