Calculating percentage increases and decreases enables a business owner to keep expenditures in line with income. Nothing paints a quicker picture of your financial health than looking at past and present earnings and expenditures, and nothing shows that more clearly than percentages.
Note your starting number. For example, in the first six months of last year, you spent $5,000 on advertising.
Compute the number for that same category in current dollars. This year, your advertising expenditures for that same period are $5,500.
Subtract the old number from the new number. In this case, $5,500 minus $5,000. You had an increase of $500.
Divide the increase ($500) by the original starting number ($5,000). The resulting decimal, 0.10 or 10 percent , is the percentage increase from last year to this year. The same formula applies to decreases.