Molecular Clock Calculator

Enter molecular clock inputs

Use observed differences for simple models. Enter transitions and transversions when using the Kimura 2-Parameter model.

Gene or dataset label

Sequence length (sites)

Observed differences

Transitions

Transversions

Clock rate (substitutions/site/Myr/lineage)

Rate uncertainty (%)

Lineage factor

Distance model

Optional calibration time (Myr)

Example data table

Dataset	Length	Differences	Transitions	Transversions	Rate	Model	Estimated Time
Cytochrome b	1,500	45	25	20	0.0025	Jukes-Cantor	6.21 Myr
COI Segment	900	18	10	8	0.0018	Kimura 2P	5.79 Myr
rRNA Region	2,000	60	31	29	0.0012	Uncorrected	12.50 Myr

These rows are illustrative. Real analyses depend on alignment quality, model fit, and a defensible calibration rate.

Formula used

1) Uncorrected p-distance

p = D / L

D is observed differences. L is aligned sequence length.

2) Jukes-Cantor correction

d = -3/4 × ln(1 - 4p/3)

This corrects for multiple hidden substitutions at the same site.

3) Kimura 2-Parameter

d = -1/2 × ln(1 - 2P - Q) - 1/4 × ln(1 - 2Q)

P is transitions per site. Q is transversions per site.

4) Divergence time

T = d / (r × f)

d is evolutionary distance, r is clock rate, and f is the lineage factor.

When two descendant lineages accumulate substitutions independently, use a lineage factor of 2. For one lineage traced from an ancestral reference, use 1.

How to use this calculator

Enter a gene or dataset label to identify the analysis.
Provide aligned sequence length and total observed differences.
Add transitions and transversions when you want a Kimura estimate.
Enter the mutation rate in substitutions per site per million years per lineage.
Choose the correct lineage factor for your evolutionary scenario.
Select the preferred distance model.
Optionally enter rate uncertainty and a fossil or geological calibration age.
Press calculate to show results, compare models, and export your output.

Frequently asked questions

1) What does a molecular clock estimate?

It estimates when two sequences or lineages diverged by combining sequence change with an assumed substitution rate. The result is an approximation, not a direct fossil date.

2) Why use correction models instead of raw differences?

Raw differences can underestimate age because some sites may mutate more than once. Correction models try to recover hidden substitutions and improve distance estimates.

3) When should I use the Kimura 2-Parameter model?

Use it when you know transitions and transversions separately. It is useful because those mutation types often occur at different rates in real DNA datasets.

4) What is the lineage factor?

It adjusts the time equation for how many lineages are accumulating substitutions. Sister lineages usually need factor 2. One evolving lineage from a reference usually needs factor 1.

5) What unit should the mutation rate use?

This calculator expects substitutions per site per million years per lineage. Keep the rate unit consistent with the interpretation of your divergence time output.

6) Why does a model sometimes return no value?

Very large observed divergence can violate the mathematical limits of some correction formulas. That usually signals saturation, poor fit, or a need for another model.

7) What does the uncertainty range show?

It shows how the divergence estimate shifts when the rate varies by the percentage you entered. Faster rates produce younger dates, while slower rates produce older dates.

8) Can this replace full phylogenetic analysis?

No. It is a quick estimation tool. Robust evolutionary dating usually requires alignments, model testing, calibration strategy, tree inference, and sensitivity analysis.