@SGaist said in Can I charge customer to use Software if I have created Software using open source Qt?:
Also, if you do any changes to Qt for one reason or another, you have to publish these changes.
In addition to what @SGaist said: You need to have the source code of the Qt version that you used. You can either provide a written offer valid for at least 3 months for your customer to request the Qt source code (not your own source code). Or you provide the Qt source code in the same way as your software (if your software can be downloaded, place a download link to the Qt source code in the same place). A download link to someone else hosting the same Qt source code does not count. You have to host it in the same place as your software.
Furthermore, the LGPL requires that the user is able to relink with a different Qt version. If you are using Qt's DLLs this is taken care of already as the user can just replace the DLLs.