The Coin Jar Examined: What a Year of Hoarded Change Costs Against Even a Modest Deposit Rate

The household coin jar is defended as harmless thrift: change that would be frittered away is instead gathered. This paper prices the jar against the obvious alternative — depositing the same stream monthly into an account paying 4.0% while inflation runs at 3.0% — for a stated change stream of USD 1.85 a day. After ten years the jar holds USD 5376.49 (after a stated 8% of its contents is lost, spent informally or never redeemed) while the account holds USD 8291.54: a gap of USD 2915.05, or 43.1% of everything contributed. At three years the gap is USD 364.34, confirmed by a stochastic check (median USD 500.92). The jar's cost is not catastrophic, but it is not zero, and it grows with the horizon: the claim that idle cash at home is a neutral place to keep savings does not survive arithmetic. The study is simulated, not measured. SIMULATED, NOT MEASURED.