[throw] money out (of|) the window

to wastefully and recklessly spend money

The origin of the idiom "throw money out the window" is not definitively known, but it likely comes from the image of someone wasting money in a reckless or extravagant manner. This phrase is used to describe wasteful spending or extravagance without obtaining any valuable return or benefit.

He felt like he was throwing money out of the window when he realized how much he spent on subscription services he rarely used.
Instead of saving for the future, she was throwing money out of the window on unnecessary luxury items.
The company's poor financial management resulted in throwing money out the window, leading to bankruptcy.
The extravagant wedding seemed to be an event where they were throwing money out of the window without considering practicality.