Compound Interest Calculator
Calculate how your savings or investment grows with compound interest, including optional recurring contributions, annual or monthly compounding, and total interest earned.
Calculator Inputs
Sets the currency this calculator's numbers are denominated in. This is presentation only — it does NOT convert your numbers between currencies, it only changes how they're formatted.
The lump sum you're starting with.
How much you add at the end of each compounding period (e.g. each month, if compounding monthly). Enter 0 for no recurring contributions.
The nominal annual interest rate (e.g. 5 for 5%). Not an effective/APY rate.
How often interest is calculated and added to your balance.
How many years (and optionally months) your money grows for.
Additional months (0-11). For 18 months, enter 1 year 6 months.
- Final Accumulated Balance
- $31,998.32
- Total Principal Contributed
- $22,000.00
- Total Interest Earned
- $9,998.32
Year-by-Year Growth Schedule
Balance at the end of each year, from year 0 to year 10.
| Year | Principal & Contributions | Interest Earned | Balance |
|---|---|---|---|
| 0 | $10,000.00 | $0.00 | $10,000.00 |
| 1 | $11,200.00 | $539.50 | $11,739.50 |
| 2 | $12,400.00 | $1,168.01 | $13,568.01 |
| 3 | $13,600.00 | $1,890.06 | $15,490.06 |
| 4 | $14,800.00 | $2,710.44 | $17,510.44 |
| 5 | $16,000.00 | $3,634.20 | $19,634.20 |
| 6 | $17,200.00 | $4,666.60 | $21,866.60 |
| 7 | $18,400.00 | $5,813.23 | $24,213.23 |
| 8 | $19,600.00 | $7,079.91 | $26,679.91 |
| 9 | $20,800.00 | $8,472.79 | $29,272.79 |
| 10 | $22,000.00 | $9,998.32 | $31,998.32 |
Principal & Contributions vs. Interest Earned
How much of your balance is money you put in (principal plus contributions) versus interest earned from compounding, at the end of each year.
- Principal & contributions
- Interest earned
About these results
CalcSpectrum calculators produce automated estimates using established formulas and the specific values you enter. Because real-world outcomes depend on input accuracy, mathematical assumptions, and rounding conventions, please verify critical figures with an appropriately qualified financial, tax, medical, legal, or other professional, as relevant.
Financial Notice: These figures are informational estimates for personal planning only. They do not constitute financial, investment, tax, or legal advice, nor do they represent a lending offer or credit approval. Provider and financial institution figures, rates, fees, and underwriting requirements may differ.
How It's Calculated
Formula
Compound interest is interest calculated on both your original balance and on interest you've already earned, so growth accelerates over time instead of staying flat. This calculator projects how an initial principal grows under compound interest, optionally adding a fixed deposit at the end of every compounding period. Each deposit is applied at the end of its period (an "ordinary annuity") — a deposit made at the end of month one doesn't start earning interest until month two. Choose annual or monthly compounding, enter the nominal annual rate and duration, and the calculator returns your final balance, how much of that is money you put in, and how much is interest earned on top of it.
Worked Examples
Lump sum only: $10,000 principal, 5% annual rate, monthly compounding, 10 years
- Periodic rate r/n = 0.05 / 12
- Total periods n·t = 12 × 10 = 120
- FV = 10000 × (1 + 0.05/12)^120 ≈ $16,470.09
- Total principal contributed = $10,000 (no recurring deposits); total interest earned ≈ $6,470.09
Recurring deposits, no starting balance: $0 principal, $100/month, 6% annual rate, monthly compounding, 5 years
- Periodic rate r/n = 0.06 / 12 = 0.005
- Total periods n·t = 12 × 5 = 60
- FV = 100 × [((1.005)^60 − 1) / 0.005] ≈ $6,977.00
- Total principal contributed = 60 × $100 = $6,000; total interest earned ≈ $977.00
Frequently Asked Questions
When do my deposits start earning interest?
Each periodic deposit is credited at the end of its compounding period, not the beginning. That means a deposit made during the current period doesn't earn interest until the next period begins. This convention (an "ordinary annuity") is the standard default used in most savings and investment calculators.
What's the difference between annual and monthly compounding?
Annual compounding calculates and adds interest once a year; monthly compounding does it 12 times a year. For the same nominal annual rate, monthly compounding produces a slightly higher final balance, because interest starts earning its own interest sooner and more often.
Should I enter my bank's APY or the nominal rate?
Enter the nominal annual rate — the stated rate before any compounding effect is factored in (e.g. "5" for 5%). This calculator derives the actual per-period rate itself based on your chosen compounding schedule, so entering an already-compounded APY would double-count the compounding effect.
Can I model a one-time investment with no ongoing deposits?
Yes — set the periodic deposit to 0. The calculator then computes pure compound growth on your initial principal alone, with no annuity contribution term.
Why is "total interest earned" not just balance minus what I typed in?
It is exactly that: total interest earned equals the final accumulated balance minus total principal contributed, where total principal contributed is your initial principal plus every periodic deposit you made. It isolates the growth that compounding itself produced, separate from money you actually deposited.