Cell Viability Decay Calculator

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

Common Tip Percentages

General Household Budget Ratios (50/30/20 Rule)

Common Measurement Conversions for Everyday Use