Definition
A phrase indicating that since one has started or become involved in something, they should complete it, even if it has become more difficult or complicated than initially anticipated.
I only intended to help a little with the project, but now that I've started, I'm in for a penny, in for a pound, and I'm going to finish it.
We've already spent a lot on renovating the house; now that we’ve gone this far, we might as well be in for a penny, in for a pound and complete the entire renovation.
He originally just wanted to try making a video, but now he’s decided to be in for a penny, in for a pound, and do his absolute best.