In for a penny, in for a pound
Definition 1 of 1
Pro Tip 1/3Full Commitment
Use this phrase to show determination to see a task through, no matter the challenges. 
We're halfway up the mountain, in for a penny, in for a pound.
Pro Tip 2/3Financial Origin
Originally referred to the British currency, implying a small risk escalating to a larger one. 
I bet £10 on the game, but with such odds, in for a penny, in for a pound—I'll bet £50.
Pro Tip 3/3British Usage
More common in British English, so be aware of your audience when using it. 
He decided to study in the UK for a semester and ended up getting a degree—in for a penny, in for a pound.