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Covid-19 test calculator
How to interpret test results
© 2020 BMJ Publishing Group Ltd.
Interactive
Pre-test probability
The likelihood a person
has covid-19 based on
their characteristics
%
Test sensitivity
The proportion of
patients with covid-19
who have a positive test
%
Test specificity
The proportion of
patients without covid-19
who have a negative test
%
If 100 people were tested with these values
Have covid-19
Do not have covid-19
True positive
False positive
False negative
True negative
Test
positive
Test
negative
They are appropriately told
to self-isolate
They are told they do not need to
self-isolate and are safe to go out
They are told they do not need to self-isolate
so they go out and infect more people
They are told they need to self-isolate
when they would be safe to go out
Probability
of having
covid-19
if test is
positive
Probability
of having
covid-19
if test is
negative
56
19
1
24
98%
56%
people who test
positive have covid-19
people who test negative
have covid-19
person who tests positive
does not have covid-19
people who test negative
do not have covid-19
Adjust these values to
update graphic below
%
%
%
Please enter a number
between 0 and 100
Please enter a number
between 0 and 100
Please enter a number
between 0 and 100