🧬

Mitotic Index Calculator

Calculate the mitotic index from cell counts in prophase, metaphase, anaphase, telophase and interphase, and estimate how long each phase of the cell cycle lasts from the total cycle time.

Cells in prophase

Cells in metaphase

Cells in anaphase

Cells in telophase

Cells in interphase

Length of the whole cell cycle

Loading calculator…

How it works

mitotic index = (cells in prophase + metaphase + anaphase + telophase) ÷ total cells × 100% · estimated phase duration = (cells in that phase ÷ total cells) × length of the cell cycle

The mitotic index is the share of cells in a sample that are dividing at the moment it is fixed. It is a standard measure of proliferation in root-tip squash practicals (onion or garlic), in tumour grading and in toxicity tests. If cells are dividing asynchronously, the fraction of cells in a phase is proportional to how long that phase lasts, so the counts also estimate phase durations when the cell-cycle length is known. Count at least a few hundred cells from several fields of view for a reliable figure.

Worked example

In an onion root-tip squash you count 40 cells in prophase, 15 in metaphase, 8 in anaphase, 12 in telophase and 425 in interphase — 500 cells in total. 75 are in mitosis, so the mitotic index is 75 ÷ 500 × 100 = 15.00%. With a 24 h cell cycle, mitosis lasts about 0.15 × 24 = 3.60 h and prophase alone about 1.92 h.

Sources: Wikipedia — Mitotic index · Science & Plants for Schools (SAPS) — Root tip squash

Frequently asked questions

What is the mitotic index?

The percentage of cells that are in mitosis (prophase, metaphase, anaphase or telophase) out of all the cells counted. A high index means rapid cell division.

Where is the mitotic index highest in a root?

In the meristem just behind the root cap, typically 10–20% in onion roots, falling towards zero in the elongation zone.

How do I estimate the length of each phase?

Multiply the fraction of cells in that phase by the total cell-cycle time. If 8% of cells are in prophase and the cycle takes 24 h, prophase lasts about 1.9 h.

Should cytokinesis be counted as mitosis?

Most practicals count telophase cells, including those with a forming cell plate, as dividing. Whatever you choose, apply it consistently and state it in your method.

Related calculators

Cell Doubling Time Calculator

Calculate the doubling time of a growing cell culture from an initial count, a final count and the elapsed time, plus the number of doublings and the specific growth rate.

Generation Time Calculator

Find the generation (doubling) time of a growing population from its starting and final size over a measured interval, plus the number of generations and the growth rate constant.

Hemocytometer Cell Count Calculator

Turn hemocytometer (Neubauer) counts into cells per mL and total cells — any square size, dilution factor or trypan blue mix volumes, live/dead viability, counting error and a seeding plan with the volume to pipette.

Surface Area to Volume Ratio Calculator

Calculate the surface-area-to-volume ratio of a sphere or cube and see why small cells exchange materials with their surroundings far more efficiently.

Chi-Square Test for Genetic Ratios Calculator

Test observed offspring counts against an expected Mendelian ratio (3:1, 1:2:1, 9:3:3:1, 1:1 or custom) — χ², degrees of freedom and p-value.

This calculator is for educational purposes. Double-check important results before acting on them.