The correct form is "didn't use to," not "didn't used to." When you make the past tense negative, you drop the -d from "used" and let "didn't" carry the past tense for you.
This is one of those grammar rules that trips up even confident English speakers because it looks wrong at first. Your brain wants to write "didn't used to like broccoli," but that double-past-tense construction does not exist in English. Once you understand the pattern, you will use it correctly without thinking.
Why "Didn't Use To" Is Correct
The structure works like this: "didn't" already marks the past tense, so "use to" stays in its base form. You are not adding -ed to "use" when "didn't" is already doing that job. Think of it the same way you would say "I didn't like broccoli" in a single sentence. You do not write "I didn't liked broccoli." The past tense marker (didn't) comes once, and the main verb stays clean.
When you use "used to" in a positive statement, the -d is part of the phrase: "She used to like broccoli." But the moment you flip it to negative, that -d disappears. The rule is simple once you see it: in questions and negatives, "use" stands alone, and "did" or "didn't" carries the tense.
The Difference Between "Didn't Use To" and "Wouldn't"
You might hear someone say "She wouldn't like broccoli when she was younger" and think it means the same thing, but it does not. "Wouldn't" suggests she refused to eat it, that she chose not to. "Didn't use to like" simply says she did not have the taste for it back then. The meaning shifts from habit to reluctance.
Use "didn't use to" when describing something that was simply not your preference or routine in the past. Use "wouldn't" when someone actively refused or resisted something. This distinction matters if you want to sound natural and be understood clearly.
How to Lock This Into Your Memory
The best way to remember the pattern is to say it aloud a few times. "I didn't use to drink coffee. My brother didn't use to play football. We didn't use to live here." Hearing yourself say the correct form builds muscle memory faster than reading about it. When you open your mouth to speak, the right version will come out.
Practise with a native speaker and you will catch yourself before you make the mistake. Speaking time is where real learning happens. In a conversation, you get immediate feedback. Someone speaks English every day and hears the rhythm of "didn't use to" naturally. When you practice with them, you stop translating grammar rules in your head and start feeling the language.
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