A Dollar Is Not Always a Dollar
Standard economics has a simple rule: money is fungible. A dollar in your savings account is identical to a dollar found on the street. But Richard Thaler's research on mental accounting reveals that humans systematically violate this principle. We partition money into mental categories — rent, groceries, entertainment, savings — and spend from each account according to different rules. This simulation visualizes how identical amounts of money are treated completely differently based on their source.
Windfall vs Earned Money
The simulation compares two $200 amounts: one from a windfall (lottery, tax refund, unexpected bonus) and one from regular earnings (salary). Watch the animated money flow: windfall dollars rush toward entertainment and impulse purchases, while earned dollars are carefully allocated to necessities and savings. The spending difference is typically 25-40% — a massive violation of fungibility that classical economics cannot explain.
The Envelope System
Mental accounting is visualized here as separate envelopes. Each envelope represents a mental budget category: necessity, entertainment, and savings. Money enters from the top (windfall in green, earned in blue) and flows to different envelopes at different rates. The bar chart below shows spending allocation for each source. The 'rational difference' output is always 0% — reminding you that any difference in treatment is psychologically driven, not economically rational.
Financial Awareness
The fungibility awareness slider models financial sophistication. Trained economists and financial professionals show smaller mental accounting effects — but never zero. Even experts maintain separate mental accounts and make systematically different decisions based on the framing of equivalent financial positions. This is why automatic payroll deductions for retirement savings are so effective — they prevent the money from ever entering a 'spendable' mental account. Understanding mental accounting is the first step to making more rational financial decisions.