Incidence Rate Calculator

Created by Dominika Śmiałek, MD, PhD candidate
Reviewed by Dominik Czernia, PhD and Jack Bowater
Last updated: Jan 09, 2023

Imagine you need to perform some statistical analysis for your study, and part of that is finding out what the incidence rate is. If this is the case, use our incidence rate calculator to determine the individual probability of getting a disease*, based on a population sample.

All you need to know is two factors, specified in the article below. There, you can also find incidence definition, incidence rate formula, and information on how to calculate the incidence rate. You may also find useful the probability calculator.

We try our best to make our Omni Calculators as precise and reliable as possible. However, this tool can never replace a professional doctor's assessment. If any health condition bothers you, consult a physician.

Incidence definition & morbidity definition

Incidence is a way of determining a person's probability of being diagnosed with a disease (A.K.A. a morbidity) during a given time. Therefore, the incidence definition is the number of newly diagnosed cases of a disease.

As we mentioned above, morbidity, a term closely related to incidence, is commonly known as a disease. One person can have more than one morbidity, e.g., hypertension and Parkinson's disease. We often confuse the morbidity definition with mortality, but morbidity DOES NOT mean deaths*.

Epidemiology makes use of both of these terms. What is epidemiology? Find out below!

Incidence rate formula: How to calculate incidence rate?

The incidence rate definition is the number of new cases of a disease divided by the number of persons at risk of the disease. What is that frequency measured in? It is the number of new cases that appear in a population of a specific size in a specific time. In medicine, we most often recalculate data so that the model's population size is 100,000 and the specific time is one year.

incidence rate = number of new cases / population at risk * population size

Let's go over an example: During one year, 12 men out a population of 50,000 healthy men were newly diagnosed with colorectal cancer. Thus, our population size is 50,000. Then, the colon cancer incidence rate equals 24 per 100,000 men per year.

The likelihood calculated with the incidence rate can help scientists anticipate future incidents and make the proper plans, such as the number of hospital beds needed and the amount of doctors with specialist knowledge required so that everyone gets the proper treatment.

What is epidemiology?

Epidemiology analyses the who, when, where of any disease and any state of health. It aims to build and improve public health, clinical research, and preventive healthcare by estimating risk factors and other characteristics that may have an influence of the spread of a disease. Public health and building strategies for preventing and treating diseases at the population level are based on epidemiological knowledge.

Incidence rate calculator

To use this incidence rate calculator, you need to know three pieces of information:

  • The total number of new cases of a specific disease that appeared over determined amount of time (most often, one year);
  • The total population at risk of getting the disease (for more information on how many participants are needed for a study check the sample size calculator); and
  • Per what population size you want to recalculate the incidence rate for. In medicine, we most often use per 100,000 people.

Once you have provided all of the fields above, the result is the incidence rate, calculated by the simple incidence rate formula you can find above. As with all of our calculators, you can input any 3 variables to find the missing one.

As a default, we calculate here how many cases would appear annually for every 100,000 people in a population.

What is incidence rate? An example.

Now that you know how to calculate the incidence rate - it's time to practice. Imagine you have a study on breast cancer. In a group of 50,000 healthy women, one got a diagnosis of breast cancer during one year. To calculate the incidence rate, we use this incidence rate calculator:

  • Total number of new cases = 1; and
  • Total population at risk = 50,000.

Thus, the solution from the incidence rate definition is:
1 / 50,000 * 100,000 = 2

It means that the incidence rate of new diagnoses of breast cancer in this population is 2 per 100,000 women per year. For more information on that matter, we recommend checking the breast cancer risk calculator.

Dominika Śmiałek, MD, PhD candidate
Total number of new cases
Total population at risk
Incidence rate
I want to calculate for a different population size
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