That's how I do it. I don't have a 6+ figure salary, or tons of disposable income, so I can't afford to give 10% of my income without reducing how much I put into savings. One thing I do have is more time on my hands than the average person. So for things like open source projects that I benefit greatly from, I always try to give some portion of my time with things like improving documentation, always submitting detailed bug reports, or writing updated versions of tutorials that are out of date.