You can use the following methods to add a subtitle to plots in ggplot2:

Method 1: Add Subtitle

p +
  labs(title='My Title', subtitle='My Subtitle')

Method 2: Add Multi-line Subtitle

p +
  labs(title='My Title', subtitle='My Subtitle Line1nLine2nLine3')

Method 3: Add Subtitle with Custom Font

p +
  labs(title='My Title', subtitle='My Subtitle Line1nLine2nLine3') +
  theme(plot.subtitle=element_text(size=18, face='italic', color='red'))

The following examples show how to use each method in practice with the following data frame in R:

#create data frame
df <- data.frame(hours=c(1, 2, 2, 3, 4, 6, 7, 7, 8, 9),
                 score=c(76, 77, 75, 79, 84, 88, 85, 94, 95, 90))

#view data frame
df

   hours score
1      1    76
2      2    77
3      2    75
4      3    79
5      4    84
6      6    88
7      7    85
8      7    94
9      8    95
10     9    90

Example 1: Add Subtitle in ggplot2

The following code shows how to add a one-line subtitle to a scatterplot in ggplot2:

library(ggplot2)

#create scatter plot with subtitle on one line
ggplot(df, aes(x=hours, y=score)) +
  geom_point(size=2) +
  labs(title='Hours Studied vs. Exam Score',
       subtitle='Data Collected in 2022')

Notice that a one-line subtitle has been added directly below the plot title.

Example 2: Add Multi-Line Subtitle in ggplot2

The following code shows how to add a multi-line subtitle to a scatterplot in ggplot2:

library(ggplot2)

#create scatter plot with subtitle on multiple lines
ggplot(df, aes(x=hours, y=score)) +
  geom_point(size=2) +
  labs(title='Hours Studied vs. Exam Score',
       subtitle='Data Collected in 2022nUniversity A Exam Scores')

By using the line break syntax ( n ) we are able to create a multi-line subtitle.

Example 3: Add Subtitle with Custom Font

The following code shows how to use the theme() function in ggplot2 to add a subtitle with a custom font size, style, and color:

library(ggplot2)

#create scatter plot with subtitle that has customized font
ggplot(df, aes(x=hours, y=score)) +
  geom_point(size=2) +
  labs(title='Hours Studied vs. Exam Score',
       subtitle='Data Collected in 2022nUniversity A Exam Scores') +
  theme(plot.subtitle=element_text(size=18, face='italic', color='red'))

Notice that the subtitle now has a font size of 18, an italic style, and a red color.

Note: You can also use face=’bold’ to use a bold font style.

The following tutorials explain how to perform other common tasks in ggplot2: