# Tagged With: math

## Why I love the Rule of 72

WARNING: This post contains math. (But you knew this with a title like that.) How long will it take an investment to double? It’s a good question. And while doubling itself isn’t the most important aspect of an investment, it’s a good way to give you an intuitive sense of how well an investment is likely … Continue reading

## Is there someone at the IRS who’s a math lover?

WARNING: This post contains math. I love math. You know this. I think math is one of our world’s ways of expressing beauty. To me, there are few things more pleasing to the eye than a elegant mathematical statement. (People tend to agree on this.) And so, if for no other reason than we all … Continue reading

## How to calculate your true account balance at the end of the month

WARNING: This post contains math. How much float do you need? Well, optimally you’d have enough float such that you could cover your entire month’s expenses on day 1, just to be safe. But in general you want to have enough float in your account such that you never need to worry about the “timing” … Continue reading

## Why to use the 15% rule for saving for retirement

WARNING: This post contains math. Last time, when I talked about saving for retirement, I mentioned that I put away at least 15% of my income away in retirement. It occurred to me that some readers may feel like I’ve taken that number randomly. To be fair, I didn’t invent the number. I find it … Continue reading

## Just making sure: Mortgage interest isn’t a reason to hold on to a mortgage

WARNING: This post contains math. “When you have a mortgage, you get a tax deduction for all the mortgage interest you pay. So you shouldn’t pay down your mortgage early, because you’ll lose the tax deduction.” This is one of the most common reasons people say to not pay down your mortgage. But this is a … Continue reading

## Which is better, a tax credit or a tax deduction?

WARNING: This post contains math. This is one of those posts that is a challenge to write. Since everyone is in different places and with different levels of financial literacy, I can’t expect everyone to have the same level of understanding on certain topics. So this post is going to be totally obvious to … Continue reading

## How to choose a deductible

WARNING: This post contains math. My car was hit the other day. We got a freak snow storm here in normally-rainy Portland, and people do not know how to handle driving in this weather. (To be fair, Oregon doesn’t salt the roads after a snow storm. This feels slightly insane to me, but I guess … Continue reading

## Don’t plan for a 12% return (but earn it anyway)

WARNING: This post contains math. How much return do you expect to make on your stock market investments? (Don’t say zero.) There are those who will say that you can expect to earn a 12% return on your investments over the long term. This isn’t to say that you’ll make 12% this year, or … Continue reading

## An introduction to negative money

WARNING: This post contains a discussion of math. In these enlightened times, negative numbers aren’t a big deal. Whether it’s your favorite golfer winning the tournament with a score of -12, or even the solution to “x = 3 – 6”, most of us don’t blink when a number with a minus sign comes … Continue reading

## Ignore interest rates on debt

“This card has a 12% APR.” “My student loan is fixed at 5%.” “I can get a new car with a 0% interest loan.” Interest rates are talked about quite often when it comes to financial matters. Mostly, this is because it’s easy; the numbers are usually low, whole numbers, and those are simple … Continue reading