~なくてはいけません・~なくてはなりません・~ないといけません
Say you must do something
You’ll be able to express obligation three ways and pick the one suited to your context.

毎日、薬を飲まなくてはいけません。
mainichi, kusuri o nomanakute wa ikemasen.
What do you think this sentence means?
I have to take medicine every day.
Say that something has to be done
These patterns express obligation: “must” or “have to.” ~なくてはいけません and ~なくてはなりません are careful forms; ~ないといけません is common in conversation.
明日、早く起きなくてはいけません。
ashita, hayaku okinakute wa ikemasen.
I have to get up early tomorrow.
ここで靴を脱がなくてはなりません。
koko de kutsu o nuganakute wa narimasen.
You must take off your shoes here.
もう帰らないといけません。
mou kaeranai to ikemasen.
I have to go home now.
~なくてはいけません
Take the ない-form, remove the final い, and add くてはいけません.
行かない → 行かなくてはいけません
ikanai → ikanakute wa ikemasen
not go → must go
勉強しない → 勉強しなくてはいけません
benkyou shinai → benkyou shinakute wa ikemasen
not study → must study
起きない → 起きなくてはいけません
okinai → okinakute wa ikemasen
not get up → must get up
~なくてはなりません
Build it the same way, using くてはなりません. This often sounds a little more formal or rule-like.
薬を飲まなくてはなりません。
kusuri o nomanakute wa narimasen.
I must take medicine.
ここで待たなくてはなりません。
koko de matanakute wa narimasen.
I must wait here.
申込書を書かなくてはなりません。
moushikomisho o kakanakute wa narimasen.
I must fill out the application form.
~ないといけません
Keep the full ない-form and add といけません. This is very common in everyday speech.
もう帰らないといけません。
mou kaeranai to ikemasen.
I have to go home now.
宿題をしないといけません。
shukudai o shinai to ikemasen.
I have to do my homework.
明日は早く来ないといけません。
ashita wa hayaku konai to ikemasen.
I have to come early tomorrow.
~てはいけません vs ~なくてはいけません
They look almost the same and mean opposite things. Built on the て-form it forbids; built on the ない-form it obliges.
Must do
毎日、薬を飲まなくてはいけません。
mainichi, kusuri o nomanakute wa ikemasen.
I have to take medicine every day.
Not taking it is what is unacceptable, so you must.
Must not do
ここでタバコを吸ってはいけません。
koko de tabako o sutte wa ikemasen.
You must not smoke here.
Doing it is what is unacceptable.
毎朝、六時に起きなくてはいけません。
maiasa, rokuji ni okinakute wa ikemasen.
I have to get up at six every morning.
今日、宿題をしなくてはいけません。
kyou, shukudai o shinakute wa ikemasen.
I have to do my homework today.
この本を明日返さなくてはいけません。
kono hon o ashita kaesanakute wa ikemasen.
I have to return this book tomorrow.
13 more examples in the grammar path — free for a limited time.