question tag with used to

[googl]

Dear teacher,

how should I make a question tag here: I used to do, ...? And in negative I didn't use to do, ...?

[Alan]

Make it in the same way as any other tag-question: "I didn't use to, did I?"

[googl]

What with positive form: should I write "I used to do, usedn't I?" or "I used to do, didn't I?"?

[Alan]

Usedn't I? is archaic. Didn't I? is the correct tag-question for contemporary usage.