There have been so many discussions on this topic of side gigs among physicians. Often, these side gigs won't even come close to being as lucrative as just seeing more patients. If you're paid based off what you bill/collect/RVU's, and can find ways to be very efficient, seeing more patients is a better use of your time than side gigs if money is the main goal. Then on the side, you can do what you actually love instead of having to think about making money off of it. And as you said, put the money into simple buckets like 401k, IRA, HSA, low cost diversified index funds; if you are a 1099 and make north of 500k/yr, hire a financial advisor to help you save on taxes and create an S-Corp. Hit 2 million in investable assets for FIRE, 3-4 million in investable assets for FAT FIRE and you're gold.
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"I have always been amazed to see intraspecialty income differences that are larger than the classic interspecialty income differences. While there is an impressive difference between the average pediatrician who makes $232K and the average orthopedist who makes $511K, I know both pediatricians and orthopedists who make twice those averages."