The old-school savings jar, compounded.

The savings jar is the oldest budgeting tool in the world - drop spare coins in a jar, empty it out at the end of the year, and marvel at the total. A modern version uses a high-yield savings account instead of a jar, so the money earns interest while it sits there. This calculator projects both what you'd save and what it grows to.

The habit works because it's low-friction. 2 a day feels negligible - the price of a coffee or a pint of milk. Over a year, that's 730. Over 10 years in a 4% savings account, 8,944. The compounding is what makes the number meaningful, not the daily amount. Larger amounts (5-10 a day) push the 10-year figure into the 20,000-45,000 range.

Use the tool to set a realistic daily target. Anyone who's tried to build a sudden 500 monthly savings habit knows it rarely lasts. A 5 daily habit does, because it fits between other small spending decisions rather than replacing a big one.

Run it with sensible defaults

Using daily deposit of 2, time horizon of 10, annual interest rate of 4%, the calculation works out to 8,834.99. Nudge the inputs toward your own situation and the output recalculates instantly. The defaults are meant as a starting point, not a recommendation.

The levers in this calculation

The inputs — Daily Deposit, Time Horizon, and Annual Interest Rate — do not pull with equal force. Not every input has equal weight. Flip one at a time toward extreme values to feel which ones move the needle most for your situation.

How the math works

Daily deposit × 30 gives monthly contribution. Standard future-value annuity formula with monthly compounding. The working is transparent — you can verify every step yourself in the formula section below. No black box, no opaque "proprietary model".

Revisiting the plan

Budgets are living documents. Re-run this whenever income changes, housing changes, or you notice a recurring overrun in a category. A budget from two years ago is probably already wrong.

What this doesn't capture

Budgets are snapshots of intent. Real spending includes irregular costs: birthdays, one-off repairs, the occasional bad week. Tracking actual spending for a month before fixing any budget usually reveals 10–20% that didn't make the original plan.