သဒ္ဒါ JLPT အဆင့် N5 – သင်ခန်းစာ 19

なくちゃ (short forなくては), and なきゃ (short for なければ) are the most common colloquial abbreviations used to convey that something 'must', or 'has to' be done.
Like てはいけない (must not), なくてはいけない (must), and なくてはならない (must), these abbreviation forms can be followed by いけない, ならない, or だめ. However, they are usually omitted, without changing the meaning.
Structures like this are referred to as spoken/colloquial language. These casual variations can come across in a very similar way to words like 'gotta' in English.

• 今日(きょう)は家(いえ)の掃除(そうじ)をしなきゃだめだから、遊(あそ)ばない。
  သင့်ရဲ့ အိမ်ကို ဒီနေ့ ညှိနှိုင်းရမည်ဆိုတော့ ငါ မထွက်ပါ။
• 野菜(やさい)を食(た)べなくちゃいけない。
  ငါ ရေခဲမုန့် စားသင့်ပါတယ်။
• あっ、洗濯(せんたく)をしなきゃ。
  အံ့, ငါ အလှဆင်ပြု လုပ်ရင်ဖြစ်ပါတယ်။
• 宿題(しゅくだい)をしなくちゃ。
  ငါ အလုပ်အတု လုပ်ရမည်။

In these examples, a variety of forms have been used naturally. There is no 'most natural' form, and it will often depend on the speaker as to which they choose.
As with almost all grammatical structures, the shortest variations (not including いけない, etc.) are the most casual/used the most often.
There are several other ways that these common abbreviations can appear based on region, or even an individual speaker's preference. An example of this is なけりゃ, which is a (very) casual form of なければ.

• お前(まえ)がやらなけりゃだめだろ。
  သင် သွားရမည်! (ဘာကြောင့် သင် ပြုလုပ်ရန် မဖြစ်မနေသင့်ပါလဲ?)

In this example, we can see that some of these less common variations are used specifically by certain genders (in general). なけりゃ itself tends to be used by male speakers, and may be considered a bit rougher than なきゃ, or なくちゃ, which can be used by anybody.