Don’t have a calculator, but need a quick answer to a financial question? Here are three shortcuts: -How long will it take to double your money? Divide 72 by your annual investment return. If you are earning 8% annually on your investments, it takes nine years for your investments to double in value.   -How much does it cost to purchase an item before taxes? Multiply the cost by 1.8 if you are in the 37% marginal tax bracket, 1.7 in the 35% or 32% marginal tax bracket, 1.5 in the 24% tax bracket, 1.4 in the 22% tax bracket, and 1.2 in the 12% or 10% tax bracket. These numbers also factor in Social Security and Medicare taxes, but not state income taxes. So, if you are in the 28% marginal tax bracket and want to spend $10,000 on a vacation, it will cost $16,000 before taxes.   -How much will your retirement savings grow in 30 years? Assuming an 8% investment rate of return, add a zero to the amount. Thus, if you have $100,000 today, it could grow to $1,000,000 in 30 years. This is a handy way to look at whether it’s worth spending money on something. For instance, the $25,000 you spend on a car today could be worth $250,000 in 30 years.