First rule:

in your balance sheet or checkbook--

Debits                Credits
on the left          on the right.

When these two column totals are equal, you are solvent.


Now for investments:

The Rule of 72:

Divide 72 by the percentage number of your investment interest (such as 15 for 15%) and the result will tell you how many years your investment will take to double at that interest rate.

for example:

Interest = 15%


It will thus take 4.8 years to double your investment.

Loan Amortization

This is the way monthly payments are calculated from the principle and interest of a loan. It includes principle and interest payments only; not taxes of any sort.

P = Principle = the original loan amount
i = Interest rate as a fraction. I.e. 6% =  0.06
n = Number of years the loan will last
q = the number of times in a year a payment is made (most times it is per month)
M = the monthly payment on the loan.

A = the amount of the total loan that is still owed. If you have just got the loan, A is the total cost of the loan,                     principle and interest




You can get your monthly payment, M, by



You can tell how much principle (P) you can pay off in a certain number of years (n) by:


Pretty much when you take a house loan for 30 years, you end up paying about as much in interest as you do in loan.

Now you don't have to rely on anybody's amortization table or calculator.