Altogether is an adverb meaning completely or, taken as a whole. Together means in the same place, at the same time, or combined into one. If you can swap in overall or entirely without changing the meaning, you want altogether; if you mean with each other or as one group, you want together.
The core difference
Altogether means entirely or overall, while together describes things or people being in the same place, time, or unit.
- altogether — completely, or considering everything overall: The old bridge was altogether destroyed by the flood.
- together — in the same place or combined into one: We grew up together on the same street.
- together — in a partnership, or calm and organised: They have been together for six years now.
How to tell them apart
A handy trick: altogether is really all plus together squeezed into one word, and it keeps the sense of "all the way" — completely, entirely, or all things considered. If your sentence is really about people or objects being in each other's company, in one place, or combined, split it back into two words: together.
The mix-up shows up most often in phrases like "not altogether surprising" (meaning not entirely surprising) versus "we are all together" (meaning in the same place). Reading the sentence back with "entirely" swapped in is a quick way to check which one you need.
