Math Sucks: Here’s Your Cheat Sheet

A page for those of us who go into full-on derp mode when it comes to math and money. Find the situation you need and there’s a tool or cheat to get your answer. 

How much money did I gain or lose?
See how much up or down something is, as a number and a %.

What will my account be worth in the future?
This is how you see what something will be worth in the future if you know the yearly percentage gain (% growth) or loss. You can also see what it will be worth if you keep adding (contributing) to the amount like in a retirement account. Includes a chart.

What percentage did my investment grow per year?
Enter the starting amount, ending amount, and how long it has been invested.

How long will it take to pay off my credit card if I just make the minimum payment? How much interest will I pay?
You don’t need to enter a number for percent minimum payment and dollar amount. You just need one or the other. For APR on savings, just put 0.

How long will it take to pay off my debt if I do a Debt Snowball (Pay Smallest Debt Balance First) or Avalanche (Pay High-Interest Rate First)?
How Much Will I Save in Interest?

If you don’t know what a debt snowball (or avalanche) is, watch for the coming tutorial. It is literally a life changing strategy for people in debt. This page will show you how much quicker you will pay off the debt and how much you will save in interest payments.

Alt. Snowball/Avalanche Calculator (w/ Graph)

Easy Monthly Budget/Cash Flow Calculator or Version 2
Use whichever is easier for you

How Do I Reach My Investment Goal Calculator
Figure out required contribution amount to reach a financial goal
or annual return needed
or length of investment needed
or what the future value of the investment is if nothing changes


Calculate a quick % or fraction of something:

What is X% of something = Multiply by .X  (move the decimal place 2 digits to the left)


99% of something = Multiply by .99

125% of something = Multiply by 1.25

1000% of something = Multiply by 10.00


75% of something  (3/4th’s, Three Fourth’s) = Multiply by .75

Add 75% to something = Multiply by 1.75


66% of something (2/3rd’s, Two Third’s) = Multiply by .66

Add 66% to something = Multiply by 1.66


50% of something (1/2, Half) = Divide by 2

Add 50% to something = Multiply by 1.5


3/8th’s of something (37.5%) = Multiply by .375

Add 3/8th’s to something = Multiply by 1.375


33% of something (1/3rd, a Third) = Divide by 3

Add 33% (a Third) to something = Multiply by 1.33


25% of something (1/4th, a Fourth) = Divide number by 4

Add 25% to something = Multiply by 1.25


20% of something (1/5th, One Fifth) = Divide number by 5

Add 20% to something = Multiply by 1.2


15% of something = Multiply by .15

Add 15% to something = Multiply by 1.15


1/8th of something (12.5%) = Divide by 8

Add an eighth (1/8th) to something = Multiply by 1.125


10% of something = Divide number by 10

Add 10% to something = Multiply by 1.1


5% of something = Divide number by 20

Add 5% to something = Multiply by 1.05


1% of something = Divide by 100

Add 1% to something = Multiply by 1.01


The “Rule of 72” (Popularized by Warren Buffett)
Used to figure out how long it will take an investment to double based on the percentage that it’s growing. Note that this is just a quick estimate. It’s not intended to get exact numbers and becomes more inaccurate above 10-15%.

Divide 72 / Growth Rate % = How many years it will take to double investment.

Divide 72 / Number of years it takes for something to double = Growth Rate %


Compilation of Financial Calculators (intermediate to advanced)