What will it take to hit your savings goal?
Post your figures. The ledger works out the deposits, the years, or the final balance.
Tool № 5 · Wednesday, September 23, 2026 · free, always
The teller posts every year of the plan, and shows the work.
Savings slip · Form SG-4
A planning estimate for savers. The arithmetic is exact; the future is not.
1. Deposits are posted at the end of each compounding period.
2. Figures are rounded to the cent; the math underneath is not.
3. “Today’s dollars” divides each balance by (1 + inflation)years. Deposit columns stay in the dollars you actually pay.
Not financial advice. This page shows arithmetic, not recommendations. The return you type is an assumption, not a promise. Markets move. Talk to a licensed professional before you act on these figures.
How the math works
This is a compound interest calculator that can solve for any of its inputs: the deposit, the time, or the final balance. The slip compounds your figures once per compounding period. With annual return r, k periods a year, per-period rate i = r ÷ k, and per-period deposit d, the balance after p periods is:
FV = PV × (1 + i)p + d × ((1 + i)p − 1) ÷ i
Solving for the monthly deposit flips that around, then converts the per-period deposit back to monthly:
PMT = (goal − PV × (1 + i)p) ÷ (((1 + i)p − 1) ÷ i) × (k ÷ 12)
Solving for time runs a bisection over the number of periods, bracketed between 0 and 100 × k, for 80 rounds, then rounds up to a whole period. When the return is zero the slip falls back to straight lines: balance = PV + d × p, and time = (goal − PV) ÷ d.
With the defaults: goal $10,000, $500 saved, 7% compounded monthly, 5 years. The slip stamps $129.78 a month.
Common questions
How much do I need to save each month to reach $10,000?
With $500 already saved, a 7% annual return compounded monthly, and 5 years: $129.78 a month, posted at the end of each month. Raise the return or the years and the monthly figure falls; the slip shows the exact trade.
How does the Rule of 72 work?
Divide 72 by your annual return to estimate how many years it takes savings to double. At 7%, 72 ÷ 7 is about 10.3 years. It is a shortcut, not a quote: it assumes a steady return, which real markets never deliver.
What does “in today’s dollars” mean?
Inflation quietly shrinks what a future dollar buys. The checkbox divides each future balance by (1 + inflation)years, so $10,000 in 5 years at 2.5% inflation shows as about $8,838 today. Your deposit columns stay in the dollars you actually pay.
How long does it take to save $50,000?
From $0 saved, putting away $500 a month at a 7% annual return compounded monthly: 80 months, or 6 years 8 months. Switch the slip to the time-to-goal mode and type your own numbers for the exact figure.
Is this savings calculator financial advice?
No. The page does arithmetic on the numbers you type. The return is your assumption, not a promise. Talk to a licensed professional before you act on these figures.
Next from the ledger
Hourly to Salary Converter: type in an hourly wage and see what it means per week, per month, per year, and what lands in your bank account.
Final Grade Calculator: the exact exam score you need to keep your grade, or a projection of where you land.
Freelance Rate Calculator: type in the income you want to take home and it quotes your minimum hourly rate, with a rate card you can copy.
Rent Affordability Calculator: this rent worksheet stamps your maximum rent by the 30% rule, the comfortable 25-to-30% band, and the monthly budget your rent has to fit inside.