When are paid upgrades offered?
 

I am flying to Chicago in 2 weeks and have booked Economy Comfort seats, however ideally I would like to upgrade to business class if there is availability. How do I go about this? Are the available seats offered to you a set time before you fly? Or can I ask at check in on my return flight. Just me travelling, thank you in advance.

- If you have miles - call flying blue if there's upgrade space available
- Sometimes a week or so in advance if there's plenty of space they might offer you an upgrade in advance
- If there's space, you might be selected for an offer at OLCI
- You can ask at the airport on day of departure if there's seats available and what the price will be to upgrade. KLM desk, KLM crown lounge or maybe at gate (I don't recommend doing it at the gate though)

Any offers being actively will likely show up if you go to change your seat selection at a self-service kiosk too.

I usually get them whilst checking in online. I always make sure to check in right when the check in window opens. Had a great deal to Colombo last year where I could upgrade to bc for €300