Entry № 15 · logged Oct 3, 2026Free, no sign-upCompound Interest · Investing

No lump sum? The deposit-only ledger still bends.

Most people do not start with $10,000 — they start with a payday. Set the starting amount to zero in the slip below (it is prefilled that way) and the ledger posts what a monthly deposit alone becomes, separating every dollar you posted from every dollar growth added.

Prefilled: $0 to start, $300 a month, 7%, 20 years. The balance is deposits plus a second, quieter deposit made of interest.

The growth ledger, Form CI-15. Post a starting balance and a monthly deposit; the slip compounds interest monthly, posts the year-by-year balance, and separates what you deposited from what growth added.

What you post Starting amount ($) Already saved or invested today. Zero is a fine start — the deposit does the early work. Monthly deposit ($/mo) Posted at the end of each month, after that month’s interest.

How it grows Annual return (%) A savings account might post 4%; a diversified portfolio has averaged near 7% after inflation-free math. Returns are never guaranteed. Years Inflation (%) Only drives the “today’s dollars” line — what the final balance buys in current terms.

Year	You posted	Interest posted	Balance

Math: each month the balance earns one-twelfth of the annual return, then your deposit posts. Steady returns are a modelling convenience — real markets wander year to year, and taxes and fees are not in this ledger.

How Compound Interest Worksinterest on interest, posted month by month Rule of 72 Calculatorthe doubling shortcut, checked against the exact math Compound vs Simple Interestthe same deposit, two very different ledgers How Long to Double Your Moneydoubling time at every return, in one table Compound Interest Calculatorthe main slip: deposits vs growth, posted

From the ledger

The deposit is the engine; interest is the tailwind that becomes a second engine

With no starting balance, the early ledger is nearly all deposits — month one’s interest on a $300 posting is under two dollars. The bend comes anyway: by the second decade the balance is large enough that a single year’s interest rivals a full year of deposits, and from there growth out-posts you. The year table shows the exact year the interest column’s annual posting passes $3,600 — one year of your deposits, posted by the balance itself.

The practical lever order follows from the math: first make the deposit automatic (a missed year early costs its compounding, not just its dollars), then raise it when income rises, then worry about return. A $50 raise to the deposit at year one is worth more than the same raise at year fifteen — the slip will prove it if you run both ledgers.

Filed answers

Questions from the growth desk

Is $300 a month enough?

Enough for what is the real question — the slip posts the 20-year balance; the Savings Goal Calculator works backwards from a target to the deposit it needs.

What if I can only do $100?

Run it. At 7% over 30 years $100 a month posts a balance where interest is the majority — time does what amount cannot.

Is this investment advice?

No — arithmetic on numbers you type.

Keep going

Also in the ledger

Savings Goal Calculatorworking backwards: what a goal needs each month Emergency Fund Calculatorfund the buffer first, then let growth run Debt Payoff Calculatorcompounding works against you here — clear it first Mortgage Calculatorthe same math, wearing a loan’s clothes Subscription Audit Calculatorfind the monthly deposit hiding in your subscriptions Hourly ↔ Salary Converterwhat the paycheck funding the deposit is worth