I see a lot of “rules of thumb” suggestions in the comments (% of income, match Google/employer, etc.). I disagree with these approaches.

I recommend that you spend the requisite time to create a detailed projection of your cash flow. Try to determine how you want to use every dollar you will ever have.

A probabilistic projection will return an optimal giving range. The range may be wide, but at the very least I think this exercise will help you identify upper and lower boundaries.

Added bonus - It’s a great way to take account of your true priorities.