Calculation desk / interest & growth
Savings Growth Calculator
Estimate savings growth from an initial deposit plus regular end-of-month contributions.
Savings Growth Calculator: Project a savings balance made up of an initial deposit and equal contributions at the end of every month. See how much of the final balance comes from money paid in and how much comes from modelled interest. The calculation keeps the rate constant and uses monthly compounding over whole years. Runs 100% locally in your browser with zero server file uploads.
- Category
- Calculators
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- In your browser
- Cost
- Free · no sign-up
- Availability
- Ready to use
Projected value
$32,703.47
- Total contributed
- $25,000.00
- Estimated growth
- $7,703.47
Future value = initial deposit × (1 + annual rate ÷ 12)^months + monthly contribution × (((1 + annual rate ÷ 12)^months − 1) ÷ (annual rate ÷ 12)); contributions are end-of-month- This is an educational/planning estimate only, not personalized financial advice.
- Actual products, taxes, fees, contribution dates, and returns differ; confirm terms with the relevant provider.
- Inputs follow common calculator conventions such as initial amount, recurring contribution, time, estimated annual rate, and compounding frequency described by Investor.gov: https://www.investor.gov/financial-tools-calculators/calculators/compound-interest-calculator
- Contributions occur at the end of each month and monthly compounding is used.
Formula and worked example
Future value = initial deposit × (1 + annual rate ÷ 12)^months + monthly contribution × (((1 + annual rate ÷ 12)^months − 1) ÷ (annual rate ÷ 12)); contributions are end-of-month
A worked example with sample values:
| Inputs | |
|---|---|
| Initial deposit | $1,000.00 |
| Monthly contribution | $200.00 |
| Annual rate | 5% |
| Time | 10 years |
| Results | |
|---|---|
| Projected value | $32,703.47 |
| Total contributed | $25,000.00 |
| Estimated growth | $7,703.47 |
Initial savings plus a monthly annuity
Let P be initial deposit, C monthly contribution, r decimal nominal annual rate, i = r ÷ 12 and n = 12 × years. Future balance A = P × (1 + i)^n + C × (((1 + i)^n − 1) ÷ i). Total contributed = P + C × n; interest = A − total contributed. At i = 0, A = P + C × n.
With $1,000 initially, $200 each month, an illustrative 5% annual rate and 10 years, i = 0.05 ÷ 12 and n = 120. The growth factor is 1.647009498. Initial funds become $1,647.01 and monthly deposits grow to $31,056.46. Adding the unrounded parts gives $32,703.47. Contributions are 1,000 + 200 × 120 = $25,000, leaving $7,703.47 modelled interest.
Keep rate and deposit timing consistent
The saving inputs in Investor.gov's projection tool (https://www.investor.gov/financial-tools-calculators/calculators/compound-interest-calculator) distinguish contributions from starting principal. This page specifically assumes month-end deposits. It divides a nominal annual rate by 12; an APY must first be converted to an equivalent monthly rate because it already reflects compounding.
CFPB distinguishes loan APR from interest rate (https://www.consumerfinance.gov/ask-cfpb/what-is-the-difference-between-a-loan-interest-rate-and-the-apr-en-733/). A credit-cost APR is not an expected savings yield. The balance here is nominal money without inflation adjustment. The rule of 72 provides a lump-sum doubling approximation, while regular contributions require the annuity term shown above.
How to use it
- Enter the amounts, rate and duration shown in the worked example or your own scenario.
- Calculate to update the result and review the assumptions.
- Compare the formula and example before using the result for planning.
Privacy & limitations
Inputs and calculations stay in your browser. No values are uploaded.
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Frequently asked questions
When does each monthly deposit begin earning interest?
In this model it arrives after that month's interest has been credited, so the first contribution earns during the remaining months and the last earns no interest before the end date. Paying at the beginning of each month would give every contribution one additional period of growth.
Can I enter annual contributions or an irregular deposit schedule?
The contribution field is monthly. Dividing an annual amount by 12 describes equal monthly deposits, which can produce a different result from one annual transfer. This calculator accepts whole years and does not follow dated one-off payments or months in which saving is skipped.
Why can interest earned be negative in a savings projection?
A negative entered rate reduces the balances under the mathematical model, so the final value can be below total contributions. Fees and inflation are not automatically subtracted. Check whether your assumption represents nominal interest, a return after charges or a real return before interpreting the growth.
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