Is there a free doubling time calculator?

Yes. The 37degrees Doubling Time Calculator is free and browser-based. Enter two timepoints or a full time course (cell counts, confluence %, or OD₆₀₀) to get doubling time, specific growth rate, and number of doublings.

How do you calculate cell doubling time?

Doubling time equals the elapsed time multiplied by the natural log of 2, divided by the natural log of the ratio of final to initial cell count. The calculator does this for you and can also project forward to predict counts and time-to-target.

What is specific growth rate?

The specific growth rate (μ) is how fast a population grows per unit time during exponential growth. It equals the natural log of the final-over-initial count divided by the elapsed time, and relates to doubling time as doubling time = ln(2) / μ.

Doubling Time Calculator: free cell-culture growth rate & doubling time

Doubling time and growth rate, without the spreadsheet

Every cell-culture lab does this math constantly — how fast is the line growing, when will the flask be confluent, how many doublings since thaw — and most people still do it in a one-off spreadsheet or a half-remembered formula.

This calculator does it properly: enter two timepoints, paste a full time course for a regression fit, or project forward from a doubling time you already know. It works with cell counts, confluence %, OD₆₀₀ — anything that grows exponentially — because the math is ratio-based, so the units cancel.

Use it now

Found a bug or want a feature? Tell us — we read everything.

What it does

Two timepoints. Enter a starting value (N₀), an ending value (N), and the elapsed time. You get the doubling time, the specific growth rate (µ) in both per-hour and per-day, the number of doublings, and the fold change.

Time course. Paste a table of (time, value) rows. The tool fits a log-linear regression — the gold-standard way to get a growth rate from more than two points — and reports the doubling time, µ, and the R² so you can see how cleanly exponential your data actually is. The fitted curve is drawn over your points on a semi-log chart.

Project forward. Give a starting value and a doubling time you already know, and the tool will either predict the value after a chosen time, or tell you how long it takes to reach a target — useful for planning seeding densities and harvest days.

Outputs. Doubling time (in hours and days), growth rate per hour and per day, number of doublings, doublings per day, fold change, and (for a time course) the regression R². Copy the results or download them as CSV.

The math

All ratio-based, with time converted to hours internally:

Specific growth rate: µ = ln(N / N₀) / Δt
Doubling time: Td = ln(2) / µ
Number of doublings: n = log₂(N / N₀)
Time course: least-squares fit of ln(value) against time — the slope is µ, and R² is reported on the log-transformed fit.

Negative growth is handled too: if a culture is shrinking, the tool reports it as a halving time instead of a doubling time.

Embed it on your site

The widget is just three lines of HTML — stylesheet, mount div, and script. There’s no backend, so there’s nothing to configure.

<link rel="stylesheet" href="https://www.37degrees.io/interactive-tools/doubling-time/styles.css" />

<div id="doubling-widget-embed"></div>

<script>
  // Optional: window.DOUBLING_THEME = "light";
</script>
<script src="https://www.37degrees.io/interactive-tools/doubling-time/widget.js"></script>

That’s it — it runs entirely in the visitor’s browser. Free for typical research use. Heavy / production use? Get in touch.

Credits

Built and maintained by 37degrees. Standard exponential-growth math — no third-party libraries, no data leaves the browser.