You want to add numerical information about a model to a plot.

To add simple text to a plot, simply add an annotation. In this example, we’ll create a linear model and use the predictvals() function defined in Adding Fitted Lines from an Existing Model to create a prediction line from the model. Then we’ll add an annotation:

library(gcookbook) # For the data set

model <- lm(heightIn ~ ageYear, heightweight)
summary(model)

Call:
lm(formula = heightIn ~ ageYear, data = heightweight)

Residuals:
    Min      1Q  Median      3Q     Max
-8.3517 -1.9006  0.1378  1.9071  8.3371

Coefficients:
            Estimate Std. Error t value Pr(>|t|)
(Intercept)  37.4356     1.8281   20.48   <2e-16 ***
ageYear       1.7483     0.1329   13.15   <2e-16 ***
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Residual standard error: 2.989 on 234 degrees of freedom
Multiple R-squared: 0.4249, Adjusted R-squared: 0.4225
F-statistic: 172.9 on 1 and 234 DF,  p-value: < 2.2e-16