The reason is that … / Because … / The reason is because …
UsageIn formal workplace writing, prefer the reason is that or a direct because-clause. The reason is because is common in speech but usually duplicates the causal link.
The reason is that …
Use when
You explicitly name the reason and then give its content.
Example
“The reason for the delay is that the vendor changed its design.”
Because …
Use when
You state the cause directly without first introducing the noun reason.
Example
“The project was delayed because the vendor changed its design.”
The reason is because …
Use when
Avoid this in concise formal writing when the simpler reason is that or because construction expresses the same causal relationship.
Example
“Replace 'the reason is because' with 'the reason is that'.”
Quick check
the reason is because, the reason why is because
Usage note