This study investigates whether the neoclassical model or mental accounting better describes how earned and windfall income are treated in sharing decisions. Participants play a dictator game after earning income in real-effort task and/or receiving a windfall. I find that dictators treat marginal earned and windfall income as partially infungible, which supports mental accounting. Two-step estimates show that sharers shared 15% of a marginal windfall token and 7% of a marginal earned token. Strikingly, sharers who had income from both sources were sharply less generous with both earned and windfall income than those who had only a single source. This aspect of mental accounts has thus far received little attention. A follow-up experiment shows that two accounts must qualitatively different, not just multiple in number, to induce more selfishness.