TCID50 Calculator

This tool calculates the TCID50 (50% Tissue Culture Infective Dose) of a virus stock using either the Reed–Muench or Spearman–Kärber method. It is designed to reduce spreadsheet friction and improve consistency in routine viral titer workflows.

Why TCID50 Accuracy Matters

Reliable TCID50 values are foundational for viral load standardization, assay reproducibility, and comparing results across experiments. Small calculation errors can propagate into large differences in downstream data interpretation.

Data Input

Enter your dataset including Initial Concentration / Dilution Factor / Inoculating Volume and the number of Positive / Total wells. Ensure that the observed positives are equal or decreasing and that the totals per dilution are identical. You can enter up to 1-10 test sets.

Use consistent dilution steps, confirm scoring criteria (CPE or endpoint), and double-check the highest dilution with 100% CPE before calculation.

How to calculate TCID50

Reed–Muench Method

Step one. Calculate infection rate:

Infection rate = cumulative positive units / (cumulative positive units + cumulative negative units)

Step Two. Identify dilutions above and below 50% positive, then calculate the proportionate distance (PD):

PD = (positive above 50% − 50%) / (positive above 50% − positive below 50%)

Step Three. Calculate logID50:

logID50 = log(dilution with > 50% positive) + PD × (−log(dilution factor))

Spearman–Kärber Method

Directly estimate logID50 using the following formula:

logID50 = log(highest dilution giving 100% CPE) + 0.5 − (total number of test units showing CPE / number of test units per dilution)

Key Features

Flexible Calculation Methods:
Supports both Reed–Muench and Spearman–Kärber methods for comparison and compatibility with lab protocols.
Streamlined Data Entry:
Easy input of dilution series, inoculating volumes, and positive/total wells.
Immediate Results:
Provides logID50 instantly with transparent calculation steps.
Reliable Workflow:
Reduces transcription and formula errors common in spreadsheet calculations.
Practical Documentation:
Encourage recording sample details (strain, cell line, operator, date) for reproducibility.

Applications

Accurate viral titer determination for vaccine development and antiviral research.
Standardization of viral stocks across experimental batches.
Multi-site collaborative studies requiring consistent TCID50 measurement.