Both English phrases “regardless of whether” or “regardless whether” are correct. However, you can remove “of” along with “whether” and the meaning will still be the same. Therefore, no matter what form you use, the intention is that the outcome is irrelevant.
So, this will be fairly easy and when you use it, the right one boils down to personal choice. Having said all that, you may want to be on guard in terms of wordiness. This will be especially true if you’re writing for a publication or on social media, where brevity is king.
Same Meaning for All Three Versions
Irrespective of if you want to use, “regardless of whether,” “regardless whether” or just “regardless,” you are comparing multiple options or items that could affect the result. Alternatively, you can say it to demonstrate the result having occurred the same way with various elements. It won’t affect the decision, point in history or some other type of outcome.
Regardless of whether it snows or not, we’re still going to the symphony.
Regardless whether it snows or not, we’re still going to the symphony.
Regardless, we’re still going to the symphony even if it snows.
Proper Sentence Structure
There are several things to note between all three examples. The most obvious is using “whether” with “or not.” You cannot have one without the other. You include “not” when there’s only one item in question. This is because “whether” indicates a comparison of two or more ideas that requires quantification.
Also, when you use “regardless” without the other words, it provides a succinct sentence that’s short and to the point. But, it may not be good to keep things short when you want to compare a list of ideas, options and etc. Notice in the last example below that “or” is not required, but some kind of conjunction will be.
She will always go back to him regardless of whether he yells, screams berates, or insults.
She will always go back to him regardless whether he yells, screams berates or insults.
She will always go back to him regardless of yells, screams, berates, and insults.
In many cases, “regardless” on its own needs a preposition. These will often be “of” or “if” to provide clarification.
People will always deny the truth, regardless of how you present the facts and evidence.
People will always deny the truth, regardless if you present the facts and evidence.
People will always deny the truth, regardless of whether you present the facts and evidence or not.
People will always deny the truth, regardless whether you present the facts and evidence or not.
Ergo, you don’t have to use “regardless of whether” or “regardless whether.” They tend to be extraneous and make a sentence far too wordy and complex. This is because, in a sense, “whether” negates the use of “regardless” from the outset. However, all three versions are 100% grammatically correct and acceptable.