Money,explained.

The balance is updated once a month. Your yearly return r is turned into the equivalent monthly rate, so a 7% year really is 7% (about 0.565% a month), and each deposit lands at the end of the month.

• P is the starting amount, C the monthly deposit, n the number of months.
• “Today's dollars” divides the result by (1 + inflation)^years, so you can compare it with prices now.
• Doubling time is ln 2 ÷ ln(1 + r). The rule of 72 (72 ÷ 7 ≈ 10.3 years) is the quick mental version.
• Real markets don't return the same amount every year. Taxes and fees are not included; the fund fee calculator shows what fees do.

Looking back uses the Consumer Price Index for All Urban Consumers (CPI-U, U.S. city average, not seasonally adjusted, 1982–84 = 100) from the U.S. Bureau of Labor Statistics. The starting year uses that year's annual average; “now” is the latest monthly figure.

The average yearly rate is (CPI now ÷ CPI then)^(1/years) − 1, counting from the middle of the start year to the middle of the latest month.

Looking ahead grows your money at the interest rate and divides by inflation:

• BLS did not publish a CPI for October 2025 because of the federal funding lapse; the annual 2025 average still exists.
• The CPI is an average basket. Your own costs (rent, insurance, school fees) can rise faster or slower.

A fund's annual fee (its expense ratio) is taken as a share of your balance, every year, whether the fund went up or down. Here each year's growth is multiplied by (1 − fee):

Then the balance is built exactly like the compound growth calculator: monthly steps, deposits at the end of each month.

• “What the higher fee costs you” is the low-fee balance minus the high-fee balance at the end.
• “Share of the no-fee result” compares the high-fee balance with the same money and returns at zero fees.
• Real funds take the fee a little each day; over a year the difference from this method is a rounding error.
• Not included: trading costs inside the fund, sales loads, advisory fees and taxes. Those come on top.

Each month the card charges interest at APR ÷ 12 on the balance, then your payment comes off. Card issuers set their own minimum payment formula in the cardholder agreement; the three most common shapes are here:

• The payment is never below the “smallest minimum” (often $25 to $40) and never more than what you owe.
• If a payment doesn't even cover the month's interest, the balance never shrinks. The calculator says so instead of printing a fake end date.
• Real cards charge a daily rate on your average daily balance, so the exact cents differ a little. New purchases, fees and penalty APRs are not included.
• In the U.S., the Credit CARD Act of 2009 requires your statement to show how long paying only the minimum would take. Compare it with this.

A fixed-rate mortgage payment is the same every month. In the U.S. the monthly rate is the yearly rate ÷ 12:

• L is the amount you borrow. Total interest is payment × N − L.
• This is principal and interest only. Property tax, home insurance, mortgage insurance and HOA dues come on top.
• The history line is the monthly average of Freddie Mac's weekly Primary Mortgage Market Survey® for 30-year fixed loans. Hover or tap it to price your loan at any month since 1971.