Chapter 02 · The mechanics
How the family bank works.
A double-entry ledger underneath, three buckets on top, and a daily interest job that turns the saving bucket into a teacher. Here’s the whole machine, opened on the workbench.
01
The buckets
Three envelopes, fixed.
Spending, giving, saving. Same three for every kid, every family, every payday. The mix is yours to set; the labels are yours to translate (some families call them now, share, later); the model underneath does not change. Consistency is the teaching tool.
Day-to-day money.
Pocket cash. The kid decides what happens to it — within the limits the family sets. Defaults to half the payday.
For someone else.
A small slice for charity, gifts, or community. Giving is one-way: once allocated, the only exit is a real donation the parent confirms.
The bucket that grows.
Earns interest daily, compounded. Moving money out of saving requires asking — the equivalent of breaking the piggy bank.
02
The ledger
Every payday is a journal entry.
Under each bucket balance is a real double-entry ledger. Money never appears or disappears — it moves from one account to another, with a credit on one side and a debit on the other. The same math your accountant uses, scaled down to a single family.
| Account | Debit | Credit |
|---|---|---|
| Family bank | $5.00 | |
| Sarah · Spending | $2.50 | |
| Sarah · Giving | $1.00 | |
| Sarah · Saving | $1.50 | |
| Balanced: debits and credits sum to zero. | $5.00 | $5.00 |
03
Interest
Saving compounds, daily.
At the family's local midnight, a job posts an interest entry to each kid's saving bucket. Daily compounding, fractional-cent remainders carried in the ledger so nothing drifts. The result: most days the saving line ticks up by a cent or two, and the kid watches it happen.
| May 19 | $120.34 | +$0.03 |
| May 20 | $120.37 | +$0.03 |
| May 21 | $120.40 | +$0.03 |
| May 22 | $120.43 | +$0.03 |
| May 23 | $120.47 | +$0.04 |
04
Asking
What requires permission.
Some moves are automatic. Some require a parent. The list is short and deliberate — the boundary between the two is where most of the conversations happen.
| The move | What happens |
|---|---|
| Spending → Saving (kid) | Auto |
| Saving → Spending (kid) | Asks first |
| Giving disbursement | Asks first |
| Any spend request (kid) | Asks first |
| Any move (parent) | |
| Voiding any entry |
05
The audit trail
Posted entries are forever.
A posted entry cannot be edited. If something is wrong, a parent voids it — and the void is itself an entry, struck through but visible alongside the original. The history is append-only. The lesson is implicit: a real ledger doesn't forget.
| May 22 | Allowance · Sarah | $5.00 |
| May 21 | Snack money · Sarah | $3.50 |
| May 21 | Reverses entry #485 | $3.50 |
| May 20 | Birthday gift · Mum | $10.00 |
06
The honest part
It is not a real bank.
No money actually moves. Balances are integer cents of a configurable currency — monopoly money, but real math. We hold no funds, we are not FDIC insured, and we are not a money transmitter. We are an educational ledger. The schema leaves the door open to real balances later; nothing in the product settles cash today.