This finance calculator brings together three calculations that come up constantly in personal finance: how much savings grow with compound interest and regular contributions, what a loan's fixed payment and full amortization schedule look like, and how to convert between an effective annual rate and a nominal rate compounded several times a year. Having all three in one place avoids manual mistakes and makes it easy to compare scenarios before committing to a loan or a savings plan.
The results are a mathematical estimate meant to support planning, not a substitute for the exact terms a bank or lender will offer: always check them against the real offer, which may include insurance, fees or other costs not reflected here.
How to use
- 1Choose a tab: compound interest, loan amortization, or rate conversion.
- 2Enter the principal, term and rate, and mark whether the rate is an effective annual rate (EAR) or a nominal rate compounded m times a year.
- 3Check the result: future value, monthly payment and amortization schedule, or the equivalent rates.
- 4Export the schedule or summary to CSV to open in a spreadsheet.
What you can do
- Compound interest with regular contributions
- Loan payments and amortization schedule
- Nominal to effective rate conversion
- Export results to CSV
What each tab solves
Each tab answers a different financial question, using the same effective/nominal rate logic so the three calculations stay consistent with one another.
- Compound interest: how much a starting balance will grow with or without regular contributions, at monthly or any other frequency.
- Amortization: a loan's fixed payment (French/annuity method) and how each payment splits between interest and principal, with an optional extra payment.
- Rate converter: how to turn an effective annual rate into a nominal one (or the reverse), and into the periodic rate that matches your payment frequency.
Effective annual rate vs. nominal rate
The effective annual rate (EAR) is what money actually earns or costs over a year once compounding is factored in. A nominal rate is a headline annual rate that compounds several times a year — for example, a 12% nominal rate compounded monthly is not the same as a 12% effective annual rate; compounded monthly it works out to roughly 12.68% EAR.
- If a lender quotes a rate "compounded monthly" or similar, that's usually a nominal rate with m = 12.
- To compare two loans or two savings products fairly, always compare their effective annual rates — it's the only apples-to-apples comparison.
- The calculator converts automatically once you pick the rate type on each tab.
Tips for reading the results
Small changes in rate, term or amount can move the final figure a lot, especially over several years of compounding or on long loan terms. Before deciding, try a few different terms and rates to understand the total cost, not just the monthly payment.
- A recurring extra payment shortens a loan's real payoff time even though the scheduled payment doesn't change.
- A longer term almost always lowers the monthly payment but increases the total interest paid.
- For compound interest, contributing at the start of each period earns slightly more than contributing at the end.
Frequently asked questions
How does compound interest work?
Compound interest reinvests the interest it earns, so in the next period you earn interest on the principal and also on the interest already accumulated. That's why growth accelerates over time, unlike simple interest.
How is a loan payment calculated?
With the French (annuity) method, the most common one, the payment stays fixed for the whole term and is calculated as payment = P × [i(1+i)ⁿ] ÷ [(1+i)ⁿ−1], where P is the loan amount, i the rate per payment period and n the number of payments. Early payments are mostly interest; later ones are mostly principal.
What's the difference between an effective annual rate and a nominal rate?
The effective annual rate already accounts for compounding within the year. A nominal rate is an annual reference rate split across several periods (monthly, quarterly…) that, once compounded, produces a somewhat higher effective annual rate.
What happens if I add an extra payment to a loan?
The extra amount is deducted straight from the outstanding principal, so the loan gets paid off sooner and you pay less total interest, even though the scheduled payment stays the same. The amortization table reflects the real, shorter payoff time.
Do the results replace what a bank tells me?
No. They're a mathematical estimate useful for comparing scenarios and planning ahead, but a lender may add insurance, fees, rounding or other conditions that change the final numbers. Always check the actual offer before signing.
Can I export the amortization schedule?
Yes. The “Export CSV” button downloads the full schedule (or the summary, on the other tabs) ready to open in Excel or Google Sheets.