ほとんど vs 大体
JLPT N4 vocabulary · what is the difference?
ほとんど means "almost all" and, with a negative, "hardly any" — ほとんど食べません means you eat almost none. 大体 means "roughly, approximately" and describes an amount or an understanding that is about right, as in 大体分かりました. The negative use is the key split: ほとんど + negative is standard, 大体 + negative is not.
When to use each
ほとんど
ほとんど
Use ほとんど for a proportion close to the whole — ほとんどの人 (most people), ほとんど終わった (nearly finished). With a negative it flips to "hardly any / almost never": ほとんど見ません, ほとんどない. It can also stand before a noun with の.
私はほとんどテレビを見ません。
わたしはほとんどテレビをみません。
I hardly ever watch television.
ほとんどの学生がその本を読んでいます。
ほとんどのがくせいがそのほんをよんでいます。
Almost all of the students have read that book.
大体
だいたい
Use 大体 for an approximate figure or a rough grasp of something: 大体三十分, 大体分かりました. It answers "about how much, about how well", not "what proportion is missing", and it is the everyday word for rounding a number in speech.
駅まで大体十分かかります。
えきまでだいたいじゅっぷんかかります。
It takes about ten minutes to the station.
話は大体分かりました。
はなしはだいたいわかりました。
I've got the gist of what you said.
Sentences where only one works
お酒はほとんど飲みません。
おさけはほとんどのみません。
I hardly drink at all.
The negative forces ほとんど. 大体飲みません is not said — 大体 does not combine with a negative this way.
宿題は大体終わりました。
しゅくだいはだいたいおわりました。
My homework is roughly finished.
大体 says "broadly done, the rest is detail". ほとんど終わりました is also fine and sounds closer to "almost all of it is done", counting what remains.
パーティーには大体三十人来ます。
パーティーにはだいたいさんじゅうにんきます。
About thirty people are coming to the party.
An approximate number takes 大体 (or 約). ほとんど三十人 does not work, because ほとんど is about a share of a whole, not a rounded count.
ほとんどの人が知っています。
ほとんどのひとがしっています。
Almost everybody knows.
Quantifying a group before a noun is ほとんどの. 大体の人 exists but sounds vaguer, closer to "people in general".
Common mistakes
大体テレビを見ません。
ほとんどテレビを見ません。
For "hardly ever", the adverb has to be ほとんど. 大体 with a negative does not produce that meaning and simply sounds broken.
ほとんど五キロぐらいです。
大体五キロぐらいです。
For a rough measurement use 大体 or 約. ほとんど would suggest "nearly all of five kilos", which is not what you mean.
Frequently asked questions
Can I use ほとんど and 大体 in the same place?
For "mostly finished / mostly understood" both work and the difference is small. The two places they do not swap are negatives (only ほとんど) and approximate numbers (only 大体).
Does ほとんど mean "almost" or "hardly"?
Both — the verb decides. Affirmative ほとんど終わった is "almost finished"; negative ほとんど終わっていない is "hardly any of it is finished".
Is 大体 the same as たいてい?
No. たいてい is about frequency — "usually, most of the time" (たいてい七時に起きます). 大体 is about amount or degree.