Because I often see benefitted and benefitting, I decided it was time to check other grammar sources:
The Associated Press Stylebook
The Chicago Manual of Style
Webster’s New World College Dictionary
All five agree that you generally double the final consonant and add ed or ing to words that end with a consonant:
hop: The rabbit hopped / is hopping across the driveway.
beg: Ella begged / is begging to go to the movie.
permit: Ella’s dad permitted / is permitting her to go.
But all also agree that it’s different with benefit:
The puppy benefited / is benefiting from nutritious food.
You benefited / are benefiting from the stock market rise.
Dictionary.com and dictionarykiwi.com consider both versions acceptable: benefited or benefitted, and benefiting or benefitting. But because both sites list the single t version first, I interpret that as the preferred usage.
Microsoft Word’s spellcheck allows either form: benefited or benefitted and benefiting or benefitting.
Although I’m starting to see more of the double-t version, the single-t forms have prevailed thus far.
According to grammarly.com:
If you are in favor of spelling the past tense of benefit with one t, you are part of the majority in the United States. However, if you think that the final t should be doubled, you are definitely not alone. You can spell it either way, but be prepared; your choice might result in a friendly debate!
If you’re a student, you might already have discovered which version your teacher / professor prefers. If you’re a business professional, see if your organization has a style guide for these kinds of questions.
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