っけ (=kke) is a suffix that you use when you are trying to remember something and make sure what it is/was.

You say that when you are talking to yourself as well like me in the picture.

「あれ？何を作るんだっけ？」
= Are? Nani wo tsukurun dakke?
= Umm? What was I going to cook now? (I don’t remember.)

See the difference below?

When you ask someone where they live for the first time.

Ex. どこに住んでいるの？(casual)
= Doko ni sunde iru no?
= Where do you live (now)?

But if you already asked the same question in past and you can’t remember where they live, you say

Ex. どこに住んでいるんだっけ？
= Doko ni sunde irundakke?
=  (I asked you before but I don’t remember.) Where do you live now again?

If you simply want to ask someone how much something cost,

Ex. これ(は*)いくらだった？
= Kore (wa) ikura datta?
= How much did it cost ? (A simple question.)

But if you already asked someone how much it cost before but you don’t remember the price, you can ask again saying
 

Ex.これ(は*)いくらだったっけ？
= Kore (wa) ikura dattakke?
= How much did it cost , again? (You told me the price before but but I don’t remember.)

Note : * （は）= wa : We often omit particles in conversation.

Although it is a casual suffix, there is a polite form.　(But be careful who you use it with.)
 

Ex. これはおいくらでしたか？ (polite)
= Kore wa oikura deshitaka?
= How much did it cost?

Ex. これはおいくらでしたっけ？(casual yet polite.)
= Korewa oikura deshitakke?
= How much did it cost again?

*************
How to form :

You add it after auxiliary verbs, た(=ta)／だ(=da)／ のだ(=noda)/ んだ(=nda))/だった(=datta) /  でした(=deshita)
 

1) noun + だ(=da)＋っけ(=kke)

or

noun + だった(=datta)＋っけ(=kke)

(The politer form : noun + でした(=deshita)＋っけ(=kke) ）

Note : だったっけ(=dattakke) is considered to be a past tense. Though we sometimes use it to confirm  the future events.

Ex.1 – a )  試験は明日だっけ？
= Shiken wa ashita dakke?
= Is the exam tomorrow?

or

Ex. 1-b ) 試験は明日だったっけ？
= Shiken wa ashita dattakke? (I heard that before but I am not sure.)

They both mean the same but だったっけ(=dattakke) stresses the fact that you heard the information in past more.

(casual but politer )

Ex.1-c) 試験は明日でしたっけ？

= Shiken wa ashita deshitakke?

Ex. 2-a) マギーは犬だっけ？

= Maggie wa inu dakke?
= Maggie is a dog, right?

(casual but politer )

Ex. 2-b) マギーは犬でしたっけ?

= Maggie wa nu deshitakke?

Ex. 3-a) 次は私だっけ？(female speech)

= Tsugi wa watashidakke?
= Is it my turn now?

(casual but politer )

Ex. 3-b) 次は私でしたっけ？

= Tsugi wa watashi deshitakke?

Ex. 4-a) あの人、何て名前だっけ？

= Anohito nante namae dakke?
= What is/was that person’s (his/her) name?

(casual but politer )

Ex. 4-b) あの人のお名前は何でしたっけ？

= Anohito no onamae wa nan deshitakke?

2) Interrogative words + だ(=da)＋っけ(=kke)

or + だった(=datta)＋っけ(=kke)

(The politer form : interrogative word+ でした(=deshita)＋っけ(=kke)）

Ex. 何だっけ？
= Nan dakke?
= What was it? (I don’t remember.)

(casual but politer )

何でしたっけ？
= Nan deshitakke?

Ex. 誰だっけ？
= Dare dakke?
= Who is/was it, again? (Who was it? I don’t remember.)

(casual but politer )

どなたでしたっけ？
= Donata deshitakke?

 (politer)

どちら様でしたっけ？

=Dochira sama deshitakke?

Ex. 何時だっけ？
= Nanji dakke?
= What time is/was it, again?

(casual but politer )

何時でしたっけ？
= Nanji deshitakke?

Ex. どこだっけ？
= Doko dakke?
= Where is/was it again?

(casual but politer )

どちらでしたっけ？
=Dochira deshitakke?

3) verb + っけ(=kke)

or verb + だった(=datta) + っけ(=kke)

3-1) verb present :
 

verb present plain form + のだ(=noda) / んだ(=nda)＋っけ(=kke) 

or　のだった(=nodatta) / んだった(=ndatta) + っけ(=kke)

(The politer form : verb present plain form + のでした(=nodeshita) or んでした(=ndeshita)＋っけ(=kke)）

Note:  If you want to know more about the function of ん(=n)  go check this lesson.

When and how to use ん=n (**のです→**んです）

Ex. これどうやって食べるんだっけ？
= Kore douyatte taberun dakke?
= I forgot. How should I eat this?

Note : Again, we sometimes use　（ん）だったっけ(=(n) dattakke) to emphasize the fact you knew (heard ) the information or experienced it before.

Ex. これどうやって食べるんだったっけ？
= Kore douyatte taberun dattakke?
= How should I eat this again?  (You told me before, I have had it before but I forgot..)

(casual but politer )

食べるのでしたっけ？

= Taberu no deshitakke?

or

食べるんでしたっけ？
= Taberundeshitakke?

Ex. 会議で何を話すんだっけ？
= Kaigi de nani wo hanasun dakke?
= What do I suppose to talk about in the meeting again?

  (casual but politer )

話すのでしたっけ？

= Hanasu no deshitakke?

or

話すんでしたっけ？
= Hanasun deshitakke?

3-2) present progressive plain form + の(=no) / ん(=n)/＋だ(=da) + っけ(=dakke) 

or　verb + の(=no) /ん(=n）+ だった(=datta) + っけ(=kke)

Ex. 今、何をやっているんだっけ？
= Ima nani wo yatte irun dakke?
= What are you doing now again?

3-3) past tense 
 

verb past plain form + っけ

or  + の(=no) /ん(=n）+ だった(=datta) + っけ(=kke)

Ex. ここに前、来たっけ？
= Koko ni mae kitakke?
= Did I (we) come here before?

or

Ex. ここに前、来たんだっけ？

= Koko ni mae kitan dakke?

(casual but politer )

Ex. こちらに前来ましたっけ？
= Kochira ni mae kimashitakke?

3-4) present perfect : 

*verb past plain form + っけ(=kke)

*verb past plain form ＋んだ(=nda) + っけ(=kke)

*verb past plain form + んだった(=ndatta)＋っけ(=kke)

(The politer form : ~ ました(=mashita) + っけ(=kke)

or

〜ことがあった(=kotoga atta)+っけ(=kke)

(The politer form : ～ことがありました(=kotoga arimashita)＋っけ(=kke)）

Ex. ここに前、来たことあったっけ？
= Koko ni mae kita koto attakke?
= Have we ever been here before?

(casual but politer )

こちらに以前、来たことはありましたっけ？
= Kochira ni izen kita koto wa arimashitakke?

3-5) past progressive : 

verb past progressive  plain form +んだ(=nda)＋っけ(=kke)

or verb + （ん=n）だった(=datta) + っけ(=kke)

(politer)   past progressive plain form+の (=no) (or ん=n) でした(=ndeshita)＋っけ(=kke)

Ex. 何を話していたんだっけ？
= Nani wo hanashite itan dakke?
= What were we talking about now? ? What was I talking about now? (I forgot)

or

Ex. 何を話していたんだったっけ？
= Naniwo hanashite itan dattakke?

(casual but politer )

Ex. 何を話していたんでしたっけ？
= Nani wo hanashite itan deshitakke?

Ex. 前、トヨタで働いていたんだっけ？
= Mae Toyota de hataraite itan dakke?
= Were you working at Toyota before (You used to work at Toyota), right?
or

Ex. 前、トヨタで働いていたんだったっけ？
 = Mae Toyota de hataraite itan dattakke?

(casual but politer )

Ex.  前、トヨタで働いていたんでしたっけ？
= Mae Toyota de hataraite itan deshitakke?

(politer)

Ex. 以前はトヨタでお仕事されていたんでしたっけ？
= Izen wa Toyota de oshigoto sarete itan deshitakke?

Ex. あれ？今日はクラスがないって言わなかったっけ？
= Are? Kyou wa kurasu ga naitte iwanakattakke?
= What? Didn’t I tell you we didn’t have a class today?

(casual but politer )

Ex. 今日はクラスがないって言いませんでしたっけ？
= Kyou wa kurasu ga naitte iimasen deshitakke?

5) adjective + っけ(=kke)

5-1) i-adjective present tense :
 

i-adjective +のだ(=noda) / んだ(=nda)＋っけ(=kke)？

or

i-adjective paste tense +  っけ(=kke)？

or のだった(=nodatta) / んだった(=ndatta) + っけ(=kke)

(the politer form : i-adjective +んでした(=ndeshita)＋っけ(=kke)？）

Ex. これでいいんだっけ？
= Kore de iin dakke?
= Is this (way) OK, you think?

    (casual but politer )

いいんでしたっけ？
= iin deshitakke?

or

Ex.これでよかったっけ？
= Kore de yokattakke?

   (casual but politer )

よかったんでしたっけ？
= yokattan deshitakke?

5-2) i-adjectives past tense:
 

i-adjective past tense  ＋っけ(=kke)？

i-adjective past tense + んだ(=nda)+ っけ(kke)?

(the polite forms) :

i-adjective past tense + でした（=deshita) + っけ(=kke)

i-adjective past tense + んでした（=ndeshita) + っけ(=kke)

Ex. 彼は背が高かったっけ？
= Kare wa se ga takakattakke?
= Was he tall? (I forgot)

  (casual but politer )

彼は背が高かったでしたっけ？
= Kare wa se ga takakatta deshitakke?

5-3) na-adjective present tense :
 

na-adjecitve + だ(=da)+っけ(=kke)？

or だった(=datta) + っけ(=kke)

(politer) na-adjecitve + でした(=deshita)＋っけ(=kke)？

Ex. あの店は静かだっけ？
=Ano mise wa shizuka dakke?
= Is that place (shop, restaurant, bar, coffee shop) quiet ? (I don’t remember well.)

  (casual but politer ) 

そこは静かでしたっけ？

= Soko wa shizuka deshitakke?

Ex. ケンちゃんはこのおやつ好きだっけ？
= Kenchan wa kono oyatsu sukidakke?
= Did (Does) Ken-chan like this snack or not?

or

ケンちゃんはこのおやつ好きだったっけ？

= Kenchan wa kono oyatsu suki dattakke?

(casual but politer )

Ex.  ケンちゃんはこのおやつお好きでしたっけ？
= Kenchan wa  kono oyatsu osukideshitakke?

5-4) na-adjective past tense : 

past tense : + だったっけ？= dattakke?

(politer) na-adjecitve + でした＋っけ？

Ex.マギー先生は前からこんなにきれいだったっけ？
= Maggie sensei wa mae kara konnani kirei dattakke?
= Was Maggie Sensei this beautiful before?

  (casual but politer )

Ex.マギー先生は前からこんなにきれいでしたっけ？
= Maggie Sensei wa mae kara konnani kirei deshitakke?

In case you wonder the same thing…

はい、前からこんなにきれいでした。
= Hai, mae kara konnani kirei deshita.
= Yes, I have been this beautiful.

でも、今は前よりもっと美しくなったかもしれません。
= Demo ima wa mae yori motto utsukushiku natta kamo shiremasen.
= But I could  be even more beautiful now than before.

6) Another way to use っけ(=kke)

っけ(=kke) is not always a question.

You use it when you just remembered something and talking to yourself . I just remember something…
 

Ex. ああ、日本語がわからない時は、マギー先生がいたっけ。
= As, nihongo ga wakaranai toki wa Maggie sensei ga itakke.
= Oh, I just remembered we can count on Maggie Sensei  when don’t understand Japanese language.

Ex. そうそう、まだ卵が冷蔵庫にあったっけ。
= Sousou mada tamago ga reizouko ni attakke.
= Oh, I just remembered we still have some eggs in the fridge.

You also use っけ(=kke) when  you are remembering past events feeling nostalgic or sentimental.

Ex. 昔はよく海に家族でいったっけ。
= Mukashi wa yoku umi ni kazoku de ittakke.
= I used to go to the beach with my family.  (Good old days..)

Ex. そういうこともあったっけ…(looking back the past.)

= Souiu kotomo attakke.

= That (kind of thing) happened as well. / I have been through that as well. (Now I remember.)

Ex. 子供の頃、毎週日曜日になるとお父さんと野球をしたっけなあ。
= Kodomo no koro maishuu nichiyoubi ni naruto otousan to yakyuu wo shitakkenaa.
= I used to play baseball with my dad on Sundays when I was a child.. (Remembering the past feeling sentimental.)

*******

ところで今日、朝ご飯、食べたっけ？

=Tokoro de kyou asagohan tabetakke?
=BTW Did I have breakfast today??? I don’t remember…