Start with the general rule, because it is unusually clean. Section 101 of the Internal Revenue Code is headed "Certain death benefits," and section 101(a)(1) provides that "gross income does not include amounts received (whether in a single sum or otherwise) under a life insurance contract, if such amounts are paid by reason of the death of the insured." No reporting gymnastics, no phase-out, no income limit. A beneficiary who receives a lump sum from a life insurance policy owes no income tax on it.
The section's own opening words carry most of the qualifications: the rule applies "except as otherwise provided in paragraphs (2) and (3), subsection (d), subsection (f), and subsection (j)." Three of those listed exceptions matter in ordinary practice, and a fourth provision, subsection (c), sits outside that list and reaches the money after it has been paid.
Interest, section 101(c). "If any amount excluded from gross income by subsection (a) is held under an agreement to pay interest thereon, the interest payments shall be included in gross income." This catches the common arrangement in which a beneficiary leaves the proceeds with the insurer, including retained-asset accounts that hand the beneficiary a checkbook rather than a check. The principal stays excluded; the interest does not, and almost no consumer material says so.
Settlement options, section 101(d). If the proceeds are paid as a series of installments rather than in a lump sum, the amounts held by the insurer "shall be prorated over the period or periods with respect to which such payments are to be made," and only the prorated portion is excluded. In substance, the part of each installment representing the death benefit discounted to the date of death is tax-free and the rest is interest.
Transfer for value, section 101(a)(2). If a policy or an interest in one is transferred for valuable consideration, the exclusion is capped at "the actual value of such consideration and the premiums and other amounts subsequently paid by the transferee." The statute then carves back out several transfers, including one to the insured, to a partner of the insured, to a partnership in which the insured is a partner, or to a corporation in which the insured is a shareholder or officer. Section 101(a)(3), added later, turns that carve-back off for a "reportable policy sale," meaning an acquisition by someone with "no substantial family, business, or financial relationship with the insured apart from the acquirer's interest in such life insurance contract."
Employer-owned policies, section 101(j). Where a business owns insurance on an employee's life and is a beneficiary, the exclusion is limited to the premiums the policyholder paid unless the contract satisfies notice and consent requirements and the insured falls into one of the listed categories.
Now the point that causes more confusion than any of the above, because two different taxes are being asked about in one breath. Section 2042 brings insurance proceeds into the deceased's gross estate in two situations: "to the extent of the amount receivable by the executor," and, for other beneficiaries, to the extent of amounts receivable "under policies on the life of the decedent with respect to which the decedent possessed at his death any of the incidents of ownership, exercisable either alone or in conjunction with any other person." Incidents of ownership reach the practical powers over a policy: the right to change the beneficiary, to borrow against it, to assign it, or to surrender it. So a person can own a policy on their own life, have the beneficiary receive every dollar of it free of income tax, and still have the whole face amount counted in the estate. Whether that produces any actual estate tax is a separate question that turns on the exclusion amount, which the estate tax page carries.
Finally, the contrast that makes this page an umbrella rather than a life insurance page. An annuity death benefit gets no section 101(a) exclusion, because it is not paid under a life insurance contract by reason of the death of an insured. The beneficiary of a deferred annuity receives the contract value, and the gain over the owner's investment in the contract is ordinary income to them. A pension survivor annuity is taxed as pension income to the survivor. Employer group life pays under section 101(a) like any other life insurance, though the coverage itself may have produced taxable imputed income to the employee during life. Same phrase, four regimes.