Which income type is generally considered non-taxable?

Military personnel allowances are generally considered non-taxable because they are designed to cover the costs incurred by service members while performing their duties, such as housing and food allowances. These allowances are excluded from gross income for tax purposes, aligning with the idea that compensation for services in the military should not be taxed to the same extent as regular wages or salaries.

In contrast, Social Security benefits may be partially taxable depending on the recipient's overall income, investment income is usually fully taxable, and rental income is also subject to taxation as it is considered income derived from property rental. This distinction is important in understanding how different types of income are treated under tax law, especially for individuals in unique situations like military service.