Needn't and need too

Needn't vs Not need to

We can use needn't and not need to in the present and both mean something is not necessary.

The meaning is the same, but needn't is slightly more formal.

I needn't go to work tomorrow as it's a holiday.
I don't need to go to work tomorrow as it's a holiday.
When we use needn't and not need to in the past, the meaning is different.

Didn't need to do something means that we did not do something and it wasn't necessary.

Needn't have done something means that we did something, but it wasn't necessary.

I didn't need to go to work today, so I stayed in bed.
I needn't have gone to work today. I didn't realise it was a holiday. What a mistake!
It's fun to spend time with friends.
It's nice to see you.