Estimate compound growth with flexible contributions, compounding schedules, and beginning/end deposit timing. See totals, charts, and a detailed accumulation schedule.
%
yearsmonths
%
%
Ending balance
$54,535.20
Total principal: $45,000.00
Total contributions: $25,000.00
Total interest: $9,535.20
Interest of initial investment: $5,525.63
Interest of contributions: $4,009.56
Buying power after inflation: $47,042.54
Breakdown
Initial: 37%
Contributions: 46%
Interest: 17%
Year-by-year growth
Accumulation schedule
Year
Deposit
Interest
Ending Balance
1
$5,000.00
$1,250.00
$26,250.00
2
$5,000.00
$1,562.50
$32,812.50
3
$5,000.00
$1,890.63
$39,703.13
4
$5,000.00
$2,235.16
$46,938.28
5
$5,000.00
$2,596.91
$54,535.20
What this Interest Calculator does
This tool estimates the growth of an investment under compound interest with flexible contributions. You can start with an initial amount, add annual and/or monthly deposits, choose whether deposits are made at the beginning or end of each period, and pick a compounding schedule (daily, monthly, quarterly, semi-annually, or annually). The calculator shows the ending balance, the total amount you personally contributed, and how much of the final value came from interest. It also separates the interest earned on your initial deposit from the interest generated by later contributions, which helps you understand how much growth came from getting started versus staying consistent over time.
Results use an effective-annual-rate approach: the nominal APR and compounding frequency are converted to an effective annual rate, then to an equivalent monthly rate for simulation. That lets the calculator mix different contribution rhythms with any compounding frequency reliably. Interest can be reduced by an optional “tax on interest” setting to approximate the drag of taxes in taxable accounts. There’s also a real-value view that discounts the ending balance by the inflation rate so you can see approximate buying power in today’s dollars.
How to read the charts
The pie chart splits your final balance into three pieces: initial investment, total contributions, and total interest earned. The stacked bar chart shows the same idea year by year. The lower two segments (initial + contributions) represent money you put in. The top segment (interest) shows the growth generated by compounding. Because compounded returns build on themselves, the interest segment accelerates later in the timeline—especially when deposits happen at the beginning of the period.
Deposits at the beginning vs. end
Contributing at the beginning of the period gives each deposit one extra month (or day) in the market, which slightly improves growth for the same deposit plan. Switching from “end” to “beginning” typically increases the ending balance by about one month of interest per deposit, a small edge that compounds over years. If cash-flow permits, “beginning” is the mathematically better choice.
Compounding frequency
For a fixed APR, more frequent compounding increases the effective annual rate. Moving from annual to monthly (or daily) compounding modestly boosts growth, but the effect is often smaller than increasing the actual APR by even a few basis points or contributing a bit more each month. Use the schedule and charts to compare scenarios.
Taxes and inflation
If you invest in a taxable account, some portion of the interest may be taxed each year. The “tax on interest” setting reduces credited interest by that percentage before it’s added to the balance. The “inflation rate” setting discounts the ending balance into today’s dollars so you can compare scenarios in real terms. These are simplifications—actual tax timing varies by account and investment type—but they are useful for planning.
Practical tips
Start early, even with a small amount—the time component dominates later.
Automate contributions; consistency usually beats sporadic lump sums.
Increasing deposits annually by even 3–5% can raise the ending balance meaningfully.
If choosing between a slightly higher APR and earlier deposits, run both scenarios here—earlier deposits often win over long horizons.
Estimates only. Investment returns are not guaranteed; fees, taxes, and market fluctuations can change outcomes. Consider professional advice for tax or investment decisions.
Interest Calculator FAQs
How do I calculate simple interest?
Use I = P × r × t, where P is principal, r is annual rate (decimal), and t is time in years. Total amount is A = P + I.
How do I calculate compound interest?
Use A = P(1 + r/n)n×t. Here n is compounding frequency (12 for monthly, 365 for daily, etc.). Total interest is A − P. Add contributions to see faster growth.
What’s the difference between APR and APY?
APR is the nominal annual rate. APY includes compounding effects:APY = (1 + APR/n)n − 1. For the same APR, higher n means higher APY.
Does compounding frequency matter?
Yes. More frequent compounding slightly increases growth for savers and increases cost for borrowers. Match it to the real product (monthly for many loans, daily or monthly for savings).
How do I include monthly deposits?
Add a monthly contribution. The calculator uses an annuity formula aligned to your compounding interval, then sums principal growth and contribution growth to produce the future value.
Can this calculator estimate time to target?
Yes—set a goal amount (if available in your UI) and we’ll iterate by period; or adjust time until the future value meets your target. Compounding and contributions can dramatically shorten the time required.
Use cases & examples
1) Simple interest (short-term loan)
Borrow $5,000 at 8% simple interest for 9 months (0.75 years). I = 5000 × 0.08 × 0.75 = $300. Total due: $5,300.
2) Compound interest (no contributions)
Invest $10,000 at 6% APR, compounded monthly, for 10 years (n = 12). A = 10000(1 + 0.06/12)^(12×10) ≈ $18,194. Interest earned ≈ $8,194.
3) Compound interest (with monthly deposits)
Start with $2,500, earn 5% APR compounded monthly, and deposit $200/month for 15 years. The future value combines principal growth and the series of deposits. Depending on timing convention, you’ll reach roughly $46k–$50k, with the calculator showing exact steps and totals.