The confusion between afterall and after all is one of those errors that looks almost reasonable on the page. The phrase is spoken quickly, the two words blur together in speech, and the brain fills in the rest. But only one form is correct: after all, written as two separate words, every time.
The short answer
"Afterall" is not a word. It doesn't appear in any major dictionary, and style guides treat it as a straightforward spelling error. The correct form is always after all, two words, no exception. If your spell-checker flags "afterall," that's the right call.
What "after all" actually means
"After all" is a two-word adverbial phrase, and it carries two slightly different jobs depending on where it sits in a sentence.
First, it can mean "despite what was said or expected." You use it to signal that something happened contrary to an earlier assumption:
She came to the party after all.
Second, it can mean "considering everything" or "when you think about it." This use often introduces a reason or justification:
We should be patient. After all, this is only the first attempt.
Both uses are common. Both require two words. The phrase functions as a sentence adverb or a connective, and English doesn't merge it into a single unit the way it does with words like "nevertheless" or "altogether."
Why "afterall" feels right
English does combine "after" with other words into single units: "afternoon," "afterthought," "afterlife." That pattern makes "afterall" feel plausible. It isn't. Those compound words were formed and standardised over long periods of use. "After all" never made that journey. It stayed a two-word phrase, and the two words carry separate grammatical weight: "after" functions as a preposition and "all" as a pronoun or determiner, referencing the considerations in play.
The same impulse that creates "afterall" creates errors like "incase" instead of "in case": the writer hears one quick unit and writes it solid. The fix is the same in both cases. Keep the space.
How to use "after all" correctly
Position matters. When "after all" opens a sentence or clause, it's usually followed by a comma:
After all, nobody expected the vote to be close.
When it closes a sentence, no comma is needed:
He changed his mind after all.
It works mid-sentence too, though this is less common and usually signals a parenthetical aside worth setting off with commas:
The cost, after all, was the whole point of the argument.
None of those positions change the spelling. Two words, always.
Quick comparison: after all vs afterall
- After all (two words): correct, widely used, appears in every major dictionary.
- Afterall (one word): incorrect, not in any dictionary, flags as a spelling error.
Similar errors worth knowing
This type of error is common across English phrases that get spoken as a single breath. Confusion over past-tense forms follows a different mechanism, but the underlying cause is similar: the spoken version of the language doesn't preserve every distinction the written version requires. Slowing down and treating each word separately is usually enough to catch the mistake before it lands on the page.
If you write "after all" and wonder whether it's right, it almost certainly is. If you write "afterall" and wonder whether it's right, it isn't.
The bottom line
"After all" is two words. It always has been, and there's no style guide or dictionary that treats "afterall" as an acceptable variant. Write the space, and the phrase takes care of itself.