Financial Calculator

How Financial Calculator Works

This is a three-in-one financial calculator. The Time Value of Money (TVM) mode solves for any one of five linked variables -- N, I/Y, PV, PMT, or FV -- given the other four, the same way a financial calculator like the HP 12C or a TI BA II Plus works. The Loan Payoff mode works out a loan's monthly payment, total interest, and payoff time, including the effect of extra monthly payments. The Net Worth mode simply totals your assets and liabilities to a single net worth figure.

Formula & Method

TVM mode uses the standard annuity time-value-of-money equations relating N (number of periods), I/Y (rate per period), PV (present value), PMT (payment per period), and FV (future value), following the convention that money paid out is entered as negative and money received is positive; an "annuity due" checkbox shifts payments to the start of each period instead of the end. Loan Payoff mode uses the same reducing-balance EMI formula as a standard amortizing loan, payment = P × r × (1 + r)n / ((1 + r)n − 1), then simulates the loan month by month (adding any extra payment you specify) to total up interest paid and find the exact payoff time. Net Worth mode simply sums every asset field, sums every liability field, and subtracts: net worth = total assets − total liabilities.

Worked Example

For a $300,000 loan at 7.5% annual interest over 30 years with no extra payment, the base monthly payment works out to $2,097.64, the loan runs the full 360 months, and total interest paid is about $455,151.67. Adding just $200 extra per month to that same loan pays it off in 272 months (22 years, 8 months) instead of 360 -- about 7 years 4 months sooner -- and cuts total interest to roughly $324,370.63, a saving of about $130,781 in interest.

Frequently Asked Questions

Why are some numbers negative in the Time Value of Money mode?

TVM mode follows the standard financial-calculator sign convention: cash you pay out (like a loan's present value or a deposit's regular contribution) is entered as negative, and cash you receive (like a future payout) is positive. This is what lets the same formula correctly handle loans, savings, and annuities.

What does "annuity due" mean in the payments-at-beginning checkbox?

An ordinary annuity assumes each payment happens at the end of its period (the common case for loans). Checking "payments at beginning of period" switches to an annuity due, where each payment is made at the start of the period instead -- common for things like rent paid in advance -- which slightly changes the FV, PV, or PMT result because each payment earns or accrues interest for one extra period.

How does extra monthly payment reduce total interest on a loan?

Extra payments go entirely toward reducing the outstanding principal (since the required interest portion is already covered), so the balance shrinks faster and less interest accrues each following month. The Loan Payoff mode simulates this month by month so both the time saved and interest saved reflect the compounding effect accurately, not just an estimate.

Does the Net Worth mode account for taxes or selling costs on assets?

No -- it's a simple sum of the values you enter for assets minus liabilities, at face value. It doesn't model capital gains tax, early withdrawal penalties, or the cost of selling illiquid assets like real estate, so your true realizable net worth after selling everything could be somewhat lower.