Mental Accounting

Cousin got his Diwali bonus last October. Two lakh straight in. The TV upgrade was done by Friday. Weekend trip by Sunday. Gone by Monday morning. The same cousin SIPs twenty five thousand from his salary every month for the last six years and has never missed. Asked him the obvious question over a cup of tea. Why does the bonus money feel different from the salary money.

It is not different. The brain just labels it differently.

Richard Thaler wrote the foundational paper on this in nineteen eighty five and won the Nobel for it in twenty seventeen. He called it mental accounting. We bucket money by source rather than by purchasing power. Salary feels earned and gets routed to the SIP. Bonus feels found and gets routed to the TV. Tax refund feels free and gets routed to a weekend. Diwali envelope feels for spending and gets spent. The wallet sees four buckets. The compounding sees one rupee.

The math is easy to write down and hard to look at. Two lakh deployed at a twelve pct long run gross grows to roughly six point two lakh in ten years. Nineteen point three lakh in twenty. Sixty lakh in thirty. One bonus splurge has a thirty year invisible bill of roughly thirty times the splurge.

Three rules I would put on the fridge.

Rupees are fungible. The label on the envelope is a brain bug not a feature.

The bonus is your highest leverage compounding moment of the year. The lifestyle baseline has not adjusted to it yet. The household budget already balances without it.

Sweep windfalls into the existing SIP or portfolio inside forty eight hours. Before the brain finishes labelling the rupee as found money. Decide the sweep amount before the bonus lands, not after.

The brain calls it found money. The compounding calls it the rupee you never gave back