なくて済む means you get out of doing something: things turned out so that you didn't have to. Take the ない-form, change the final い to くて, and add , which conjugates like any う-verb. You hear it most as or , reporting something you were spared.
、。
The bus came, so I didn't have to walk.
、。
Because I had insurance, I got by without having to pay the full amount.
。
I'm glad I didn't have to move.
なくて済む or なくてもいい
gives permission: nobody requires it. なくて済む says you were spared something you expected to have to do, because of something else that happened. The thing avoided is a burden – a cost, a chore, a trip.
。
You don't have to come tomorrow.
、。
After reading the manual it was easy, so I was spared from having to ask someone.
ないで済む and ずに済む
and
mean the same. ずに済む is the most formal of the three and the usual one in writing; する becomes
.
、。
I had an umbrella, so I didn't get wet.
Usage notes
These go beyond reporting what you got out of.
Before it happens
In the non-past, なくて済む says what you'll be spared if things go a certain way, often after a ば-clause or with .
、。
If you leave early, you won't get caught in traffic.
、。
If I submit this document, I might not have to do the interview.
なくて済むように and なくて済むなら
With ように it gives a purpose, "so that you won't have to". With なら it is a condition, "if you can get out of it".
、。
Let's prepare now so that we won't have to struggle later.
、。
I'd rather not do it if I can get out of it.
Lingaku