If you forget to check in, but do check out (without having been checked on the train), then a correction fee is added to your invoice instead of the actual fare, since the actual fare could not be determined.

A correction fee will also be added to your invoice if you are found travelling on the train without having checked in, i.e. travelling without a valid ticket, but this one will be higher.

See this page for more information about correction fees.

There’s also a difference in what for subscription you have. If you’re paying for unlimited travel at certain times (I.E. weekend free) and you forgot to check in while traveling weekends, than the person checking your card will be “should be able” to see it.

If you’re caught outside of your paying subscription, than have fun paying the fine.

2 tips;

1 Download the NS app and use the check -in/-out function of the app.

2 Just don’t forget. Just like how you always lock the door in the toilet or flush after using it. It should be a habit to have your card at the ready when you enter a Station.