Project how cell viability declines over time using first-order exponential decay kinetics. Enter the starting viability, a decay rate constant, and elapsed time to get the current viability, half-life, and time until a chosen threshold.
Half-life t½ = ln(2) / k, independent of the starting viability.
Results
Calculated
Current viability
—
Viability at elapsed time t
Time to threshold
—
Elapsed time to reach the threshold
Viability half-life
—
Time for viability to fall by half
Viability lost
—
Percentage points lost over t
Ready
Set the initial viability, decay rate, elapsed time, and threshold, then press Calculate.
Add this calculator to your website
How to use this calculator
Enter the starting viability of your cell population, a decay rate constant, and how much time has elapsed, then click Calculate to project the current viability, the time remaining until a threshold is reached, and the viability half-life. Click Clear to reset all fields to the defaults.
The formula
This calculator uses first-order exponential decay, the standard model for how the live fraction of a cell population declines over time: V(t) = V0 × e^(−k×t), where V0 is the initial viability (%), k is the decay rate constant (per hour), and t is elapsed time (hours). The viability half-life — the time for viability to fall by half regardless of the starting value — is t½ = ln(2) / k. The time until viability reaches a chosen threshold is t = ln(V0 / threshold) / k.
Understanding the inputs
Initial viability is the percent of live cells at time zero, typically measured by trypan blue exclusion or a similar viability stain. The decay rate constant k is specific to a cell type and storage or process condition — it is normally estimated by fitting measured viability against time for your own cells, since it is not a universal constant. Elapsed time should use the same time unit as k (hours here). The threshold is the minimum viability your protocol or experiment considers acceptable.
Interpreting the results
Current viability is the model's projection for right now, given your inputs. Time to threshold tells you how long you have before viability is projected to drop to the minimum you specified. Half-life lets you compare decay speed across conditions independent of the starting percentage. Viability lost is simply the drop in percentage points since time zero.
Frequently Asked Questions
What formula does this cell viability decay calculator use?
It uses first-order exponential decay: V(t) = V0 x e^(-k x t), where V0 is the starting viability percentage, k is the decay rate constant per hour, and t is elapsed time in hours. This is the standard model for how the fraction of live cells in a population declines over time outside optimal conditions.
What is the decay rate constant (k)?
k is a first-order rate constant, in units of inverse hours, describing how quickly viability falls. Larger k means faster death. It is typically estimated by fitting measured viability-versus-time data from your own cells or process, since it varies by cell type, temperature, and storage conditions.
How is the viability half-life calculated?
Half-life is the time for viability to fall by half at a constant decay rate: t half = ln(2) / k. It does not depend on the starting viability, only on k, so it is a useful way to compare how fast different conditions or cell lines lose viability.
What does time to threshold mean?
It is the elapsed time at which viability is projected to fall to a threshold percentage you set (for example, the minimum viability your protocol accepts), calculated as t = ln(V0 / threshold) / k. It helps plan how long cells, samples, or a process can sit before viability drops below an acceptable level.