Key Financial Math Formulas
Financial mathematics provides tools to analyze monetary transactions and investments. Here’s an overview of essential formulas:
Simple Interest
Simple interest is calculated only on the principal amount. The formula is:
I = P * r * t
Where:
- I = Simple Interest
- P = Principal amount
- r = Interest rate (as a decimal)
- t = Time (in years)
The accumulated amount (A) after time t is:
A = P + I = P(1 + rt)
Compound Interest
Compound interest is calculated on the principal and the accumulated interest. The formula is:
A = P(1 + r/n)^(nt)
Where:
- A = Accumulated amount
- P = Principal amount
- r = Interest rate (as a decimal)
- n = Number of times interest is compounded per year
- t = Time (in years)
For continuous compounding, the formula is:
A = Pe^(rt)
Where:
- e ≈ 2.71828 (Euler’s number)
Present Value
Present value (PV) is the current worth of a future sum of money or stream of cash flows, given a specified rate of return. For a single future amount:
PV = A / (1 + r/n)^(nt)
Or, for continuous compounding:
PV = Ae^(-rt)
Annuities
An annuity is a series of equal payments made at regular intervals.
Future Value of an Ordinary Annuity
An ordinary annuity has payments made at the end of each period.
FV = PMT * (((1 + r/n)^(nt) – 1) / (r/n))
Where:
- FV = Future Value
- PMT = Payment amount per period
Present Value of an Ordinary Annuity
PV = PMT * ((1 – (1 + r/n)^(-nt)) / (r/n))
Future Value of an Annuity Due
An annuity due has payments made at the beginning of each period.
FV = PMT * (((1 + r/n)^(nt) – 1) / (r/n)) * (1 + r/n)
Present Value of an Annuity Due
PV = PMT * ((1 – (1 + r/n)^(-nt)) / (r/n)) * (1 + r/n)
Loans and Mortgages
The formula to calculate the periodic payment (PMT) on a loan is:
PMT = P * ((r/n) / (1 – (1 + r/n)^(-nt)))
Net Present Value (NPV)
NPV is the difference between the present value of cash inflows and the present value of cash outflows over a period of time.
NPV = Σ [CFt / (1 + r)^t] – Initial Investment
Where:
- CFt = Cash flow during period t
- r = Discount rate
Internal Rate of Return (IRR)
IRR is the discount rate that makes the NPV of all cash flows from a particular project equal to zero. It often requires iterative methods or spreadsheet software to calculate.
These formulas provide a strong foundation for understanding and performing financial calculations. Remember to choose the correct formula based on the specific situation and ensure you understand the variables involved.