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That's odd, because lot of these questions are actually pretty easy to answer. The IRS is good about publishing the data. Given that – and given the recent interest in personal income inequality, I decided to write a little bit about the different kinds of income people report on their tax returns. A longer paper – Sources of Personal Income – is here, but for a brief overview, you might want to check out the top ten sources of income:
Social Security — Depending upon your income, Social Security benefits might be entirely tax-free or partly taxable. Ex: If your income is more than $25,000 — or $32,000 if married filing jointly — up to 85% of your Social Security benefits is taxable. When figuring your income, include tax-free interest income and 50% of your Social Security benefits.

4. Focus first on passive income streams that you create once but they continue to generate income. For example, writing a book is a passive income stream. You write it once and sell it over and over. The word passive is a little deceptive because you need to market the book. Nevertheless, compared to non-passive sources of income, which you need to do over and over to make money, such as providing a service, passive income streams require less time once they’re created. Other forms of passive income include other written works (i.e. courses), audio or video creations, affiliate marketing, licensing your idea, franchising, or continuity programs (i.e. memberships).
You are also free to choose a fund that is based on any index that you want. For example, there are index funds set up for just about every market sector there is — energy, precious metals, banking, emerging markets — you name it. All you have to do is decide that you want to participate, then contribute money and sit back and relax. Your stock portfolio will then be on automatic pilot.
Blogs and authority websites are different than niche websites, because they generally imply on-going content generation.  Sure, I could stop writing on this blog today and let it sit forever, but that’s not the intention of the blog.  Furthermore, blogs and authority websites tend to include a community or social aspect.  We have Facebook pages and Twitter accounts (can someone explain to me why the hell I haven’t made a Facebook page yet?), and we discuss various topics in the comments of each article or blog post.  Although SEO does affect traffic, community is more important.
I formed a publishing company a number of years ago and have published a couple of technical books I’ve written since then. I doubled my goal for copies sold, but it’s definitely not enough income to retire on. Writing books is a tough area. You’ll definitely be proud of the accomplishment and seeing the sales happen around the world, but it’s tough to make it really profitable.

For a person working for a wage, their source of income is their job, or their labor (aka their time that they sell to someone). But you can own a house, and rent it out, and when your renters pay you renter every month, the source of that income check is your rental property, or your house. It would just be called rental income. If you have money in the bank in an account that pays interest, those interest payments are another source of income. We can say the source is interest payments, or we can identify the asset that is generating rent, and say your money in the bank that is generating “rent” (aka interest) is your source of income.
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