I would also want an `overdue?` method on this class:

```ruby
def overdue?
  (Time.now).to_i > book.due_date && book.status == "Checked Out"
end
```

Which would make the following line:

```ruby
if overdue?
```

You could do the same with an `available?` method, which would make this whole conditional much more readable:

```ruby
if overdue?
  ...
elsif available?
  ...
end
```