Transferrin Saturation Calculator (TSAT from serum iron and TIBC)

Understanding the transferrin saturation calculator — concept and principle

Transferrin saturation (TSAT) is the share of the blood's iron-carrying protein, transferrin, that is actually carrying iron. This calculator works it out from serum iron and total iron-binding capacity (TIBC), or from serum iron and unsaturated iron-binding capacity (UIBC). It is used to look for iron deficiency and iron overload.

Iron ÷ binding capacity: with the default inputs the result is 28.1% (within 14–50%).

How it is calculated

TSAT (%) = serum iron ÷ TIBC × 100

TIBC = serum iron + UIBC (if your report gives UIBC)

Both values must be in the same unit (µg/dL or µmol/L); the ratio does not depend on the unit.
Reference range used: 14–50% (Mayo Clinic Laboratories). Screening flags: below 16% (iron deficiency), above 45% (iron overload).

The principle

TIBC measures how much iron transferrin could carry if it were full; serum iron is how much it is carrying now. Their ratio shows how full the transport system is. When iron stores are low, the body makes more transferrin and less iron is available, so saturation falls. In iron overload, as in hereditary haemochromatosis, transferrin fills up and saturation rises.

Worked example

Default inputs: serum iron 90, TIBC 320 (µg/dL).

TSAT = 90 ÷ 320 × 100 = 28.1%.
UIBC = 320 − 90 = 230.
Within the 14–50% reference range → Yes; screening note No flag (16–45%).

Each point is the calculator re-run with only “Serum iron” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Serum iron	Transferrin saturation (TSAT)
22.5	7%
45	14.1%
67.5	21.1%
90	28.1%
112	35.2%
135	42.2%
180	56.3%

How to read the result

Where does your result fall?

A TSAT under 16% supports iron deficiency (under 20% is often used when there is inflammation or chronic kidney disease). Above 45% is typical of haemochromatosis and other iron overload and usually leads to repeat fasting tests and further checks. Ferritin is the better test of iron stores, and doctors interpret both together.

Common mistakes

Testing after an iron supplement or a meal, which raises serum iron temporarily.
Entering UIBC as TIBC.
Relying on TSAT alone without ferritin.

Keep in mind: This is not a diagnosis. Abnormal iron results should be interpreted by a doctor.

Frequently asked questions

What is a normal transferrin saturation?

Roughly 14–50% by the reference range used here; laboratories differ slightly.

Why test in the morning while fasting?

Serum iron rises after meals and varies through the day.

What does a high TSAT mean?

It may indicate iron overload such as haemochromatosis, but repeat testing and ferritin are needed.

Sources: Mayo Clinic Laboratories, Iron and Total Iron-Binding Capacity, Serum (test catalogue) · World Health Organization, Assessing the iron status of populations, 2nd ed., 2007

Checked 9 Nov 2026. Mayo Clinic Laboratories, Test Catalog “SAT — Percent Saturation” (iron ÷ TIBC × 100; reference 14–50%; < 16% iron-deficiency screening, 20% with inflammation; > 45% in hereditary hemochromatosis).

Your numbers