About the project

Rhythm analysis made accessible.

Cosinor.Online brings the classic cosinor method into a modern browser-based workspace for researchers working with time-distributed biological data.

Start an analysis Calculation manual
Classic single-component model Y = M + A × cos(2π × (t − φ) / T)

Estimate the rhythm-adjusted mean, amplitude and timing of the fitted peak.

Biological rhythms

Circadian and ultradian processes

In living systems, biological processes fluctuate over time through the integration of internal and environmental factors. Circadian oscillations of approximately 24 hours are particularly significant and widely studied in physiology.

Organisms also exhibit ultradian rhythms with periods shorter than 24 hours, including 4–6-hour cycles and approximately 90-minute sleep cycles. Quantifying these patterns can provide insight into hormonal regulation, autonomic dynamics and other time-dependent processes.

Suitable inputs

Supported data

The tool is intended for physiological time-series data such as hormone levels, activity, blood pressure or temperature.

  • Circadian and shorter ultradian periods
  • Evenly or unevenly spaced observations
  • Browser-based input without installation

Key outputs

What the model estimates

The fitted model helps quantify the central characteristics of a biological rhythm.

MESOR
Rhythm-adjusted mean
Amplitude
Distance from MESOR to the fitted peak
Acrophase
Timing of the fitted peak

Research and citation

Using Cosinor.Online in your work?

The project is maintained by Lubos Molcan, Ph.D. If you use this tool in research, please cite:

Preferred citation:
Molcan, L. (2026). CosinorOnline: A free web-based platform for cosinor analysis, validated using simulated datasets and demonstrated using cardiovascular recordings from a prenatal hypoxia model. Chronobiology International.

Earlier preprint:
Molcan, L. (2019). Time-distributed data analysis by Cosinor. bioRxiv, 805960. https://doi.org/10.1101/805960
Open peer-reviewed publication