How does inflation change the answer?

Inflation adjustment estimates future purchasing power by discounting the nominal balance with the Fisher relation, using your entered annual inflation rate.

Yes. All calculations run locally in your browser; nothing is uploaded or stored on a server.

Compound Interest Calculator — Monthly Contributions & Inflation

Plan savings and investments privately in your browser. Supports EAR/APY or nominal APR with compounding frequency.

Finance Calculator Notes

Last updated23 June 2026

Calculation reviewed23 June 2026

Prepared byStarlight Tools editorial team

This calculator is for education and planning only. It is not financial, tax, investment, or legal advice.

Inputs

Currency

Currency affects display only, not the math.

Initial Deposit

Required unless solving for starting principal. Example: 1000.

Contribution Amount

Amount added at the selected frequency. Example: 100.

Rate Type

APR needs compounding. APY/EAR already includes it.

Compounding

Used only when rate type is nominal APR.

Effective Annual Rate (EAR/APY) (%)

Enter decimals like 4.75. Range: 0 to 100%.

Custom compounds/year

Whole number from 1 to 3650.

Contribution Frequency

Contribution Timing

Time Period

years

Range: 0.01 to 100 years.

Annual Contribution Increase

Optional raise applied after each full year.

Annual Inflation

Used for purchasing-power estimates only.

Enable Inflation Adjustment
Shows nominal and inflation-adjusted values.

Results

Final Balance

—

Total Interest

—

Total Contributions

—

Effective annual rate —

Effective monthly rate —

All-time return —

Time to double —

Inflation-adjusted purchasing power —

Goal solve output —

Rate breakdown

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Growth chart

Run a calculation to draw the projected balance.

Breakdown table

View

Period	Deposits	Interest	Balance	Purchasing Power
—

Monthly view is capped at 360 rows to keep the page responsive.

Nominal and inflation-adjusted values are labelled separately; color is only decorative.

How We Calculate This

The calculator converts your entered rate into an effective annual rate, then projects growth one contribution period at a time. Contributions are added at the selected timing: beginning-of-period deposits compound for that period, while end-of-period deposits are added after that period's growth.

APR conversion: nominal APR uses the selected compounding preset. For periodic compounding, EAR = (1 + APR / m)^m - 1. For continuous compounding, EAR = e^APR - 1.
APY/EAR input: APY or EAR is already effective annually, so the compounding preset is not applied again.
Periodic growth: each contribution period uses (1 + EAR)^(1 / periodsPerYear) - 1.
Annual contribution increase: the contribution amount steps up after each full year.
Inflation: purchasing power uses the Fisher relation, (1 + nominal) / (1 + inflation) - 1, and discounts projected balances by inflation over time.
Excluded items: taxes, fees, penalties, account minimums, promotional-rate changes, and bank-specific rounding rules are not included.

All calculations run in your browser. No deposit amounts, target balances, or rates are uploaded.

Worked Examples

One-time deposit

A $10,000 deposit earning 5% APY for 10 years with no extra contributions grows to about $16,289. The extra $6,289 is compound interest.

Monthly savings plan

Starting with $1,000 and adding $250 monthly at 6% APY for 15 years produces a much larger balance than the initial deposit alone because each contribution gets its own time to compound.

Daily compounding savings account

A 5% nominal APR compounded daily has an effective annual rate of about 5.13%. Select Nominal APR and Daily to compare it with a 5% APY quote.

Inflation-adjusted return

If an account earns 7% APY while inflation is 3%, the real annual growth rate is about 3.88%, not 4.00%, because the Fisher relation compounds both rates.

APR versus APY conversion

A 12% nominal APR compounded monthly becomes about 12.68% APY. The calculator shows this converted effective rate in the result cards.

FAQ

What is the compound interest formula?

This calculator converts the entered rate to an effective annual rate, then compounds each contribution period using (1 + EAR)^(1 / periodsPerYear) - 1. Beginning-period contributions are added before growth; end-period contributions are added after growth.

What is the difference between APR and APY?

APR is commonly a nominal annual rate and needs a compounding frequency. APY, also called EAR, already includes compounding and represents the effective annual growth rate.

Does daily compounding earn more than monthly compounding?

For the same nominal APR, yes. Daily compounding usually produces a slightly higher APY than monthly compounding because interest is credited more often.

Are contributions made at the start or end of the period?

You choose the timing. Beginning-of-period contributions have one extra period to compound, so they normally produce a higher balance.

Why might this result differ from my bank?

Banks may use exact calendar days, daily balance methods, account fees, taxes, promotional rates, minimum-balance rules, or rounding that this educational calculator does not include.

Are taxes and fees included?

No. Taxes, fees, penalties, transaction costs, and account charges are excluded.

How does inflation adjustment work?

Inflation adjustment estimates purchasing power by discounting the nominal projection with your entered annual inflation rate, using the Fisher relation for the real return.

What is the difference between simple and compound interest?

Simple interest earns only on the original principal. Compound interest earns on principal plus previous interest, which is why long timelines can change the result so much.

How often should interest compound?

Use the compounding frequency stated by the account, investment, or lender. If the quote is APY or EAR, choose the effective annual option and do not apply another compounding frequency.

Is my data private?

Yes. The calculator runs locally in your browser and does not upload your entries.