All that bottled water adds up. / Elia Zane/Hemera / Getty Images
An earlier version of the story below misstated the impact of tax brackets on raises and the annual cost of bottled water.
Few subjects are as likely to generate a collective groan as math, but math is necessary — just ask math educator Laura Laing, author of Math for Grownups. Laing’s book explores everyday problems such as calculating how much a raise really is after taxes and converting calories to cardio time.
Here are a few of her tips:
If you buy three bottles of water a day, at $1 a bottle, you’ll be spending $1,095 a year. If tap water isn’t an option, a water filter can be had for about 12.5 cents a day, or $45.63 a year.
The 20% rule.
On average, a car depreciates 20% in the first year. If you can make a 20% down payment when you buy, you won’t owe more than your car is worth.
It may seem like a lifetime ago that you learned to plan a budget in high school economics class, but it’s never too late to get started. Budget experts say groceries should account for about 18% of your income, housing 28% to 33% and savings 10% to 20%.
Sizing up a raise
A hefty raise might not be as big as it looks. Extra money could bump you into the next tax bracket, which means you’ll pay a higher tax rate on earnings above a certain threshold. Relax: Your earnings below that threshold are still taxed at the previous, lower tax rate.