Best Finance Calculators 2026

Frequently Asked Questions

What is compound interest and how does it work?▾

Compound interest earns returns on both the original principal and previously accumulated interest - so your returns earn returns. Formula: A = P(1 + r/n)^(nt), where P is principal, r is annual rate, n is compounding frequency per year, t is years. At 7% annually, $10,000 grows to $19,672 in 10 years, $38,697 in 20 years, and $76,123 in 30 years. This exponential growth is why starting to invest early produces dramatically better outcomes than starting later.

How do I calculate a loan monthly payment?▾

Monthly payment = P [r(1+r)^n] / [(1+r)^n - 1], where P = loan amount, r = monthly interest rate (annual rate / 12), n = total payments. For a $200,000 mortgage at 7% for 30 years: monthly rate = 0.07/12 = 0.005833, n = 360, payment = $1,330.60. Free online loan calculators (Bankrate, NerdWallet, Investopedia) compute this instantly - also showing total interest paid over the loan life, which often exceeds the original principal.

What is a good investment return to use in financial planning calculators?▾

Common planning assumptions: US stock market (S&P 500) has returned approximately 10% average annual return historically (7% after inflation). Conservative planning uses 6-7% nominal return. Bonds historically return 3-4%. A balanced 60/40 stock/bond portfolio has returned approximately 7-8% historically. Use 6-7% for long-term retirement projections to be conservative. Actual future returns are uncertain - model multiple scenarios (pessimistic, base, optimistic) rather than relying on a single rate.

How is a monthly loan payment calculated?▾

A monthly loan payment is determined by three factors: the loan amount (principal), the interest rate, and the term (number of payments). The calculation uses an amortization formula that spreads repayment so each equal monthly payment covers the interest due that period plus a portion of the principal, with the split shifting toward principal over time. A higher rate or larger principal raises the payment, while a longer term lowers the monthly payment but increases total interest paid. A finance calculator applies this formula instantly, so you can enter the numbers and see the payment, and adjust the term or amount to find something affordable. It also reveals the total interest, which the monthly figure alone hides.

What is the difference between simple and compound interest?▾

Simple interest is calculated only on the original principal, so it grows at a constant rate over time, common in some short-term loans. Compound interest is calculated on the principal plus any interest already accumulated, so the balance grows on an ever-larger base and accelerates over time. Compounding is powerful for savings and investments, where earning interest on past interest significantly increases growth over long periods, and costly for debt, where unpaid interest compounds and the balance can grow quickly. Most savings, investments, and many loans use compound interest. A calculator shows the difference clearly, which is why understanding compounding, and starting to save early, matters so much for long-term outcomes.

Should I choose a shorter or longer loan term?▾

It depends on your priorities, and a calculator makes the trade-off clear. A shorter term means higher monthly payments but much less total interest paid, so the loan costs less overall and is paid off sooner. A longer term means lower, more affordable monthly payments but more total interest over time, so you pay more in the end for the same loan. The right choice balances what you can comfortably afford monthly against the total cost you are willing to pay. Some people choose a longer term for lower payments and flexibility, then pay extra when they can to reduce interest. Use a calculator to compare the monthly payment and total interest for different terms before deciding. This is not financial advice.