Mark-up is the amount you add to the cost to get the retail price. Let's say that you mark up an item for which you pay $3.00 by 50%. Convert the percentage to a the decimal form 0.50 and multiply $3.00 by 1.50 to get $4.50. Your mark-up is 50% because you increased the cost by 50% to get the retail price.

Following through with the same example, now we look at this in reverse. When you sell the item for $4.50 with a cost of $3.00, then you have a profit of $1.50 on a sale of $4.50. The gross profit percentage is 1.50/4.50 = 0.33 or 33%.

When you have the item, know what gross profit percentage you want, know the cost, this is the procedure to find the mark-up percentage.

Subtract the decimal form of the gross profit percentage from 1.00.	EXAMPLE: 1.00 - 0.33 = 0.67
Divide 1.00 by the result in step one.	EXAMPLE: 1.00 / 0.67 = 1.49
Multiply the result in step two by the cost to get the retail price.	EXAMPLE: 1.49 X $3.00= $4.50

Or, use this worksheet:

1. Enter 1.00	1.
2. Enter the gross profit percentage you want in the form of a decimal (0.50, not 50%).	2.
3. Subtract line 2 from line 1.	3.
4. Divide 1 by the amount in line 3.	4.
5. Enter the cost of the item.	5.
6. Multiply line 4 by line 5. This is your sale price.	6.

Expressed algebraically, where "M" is the multiplier and "G" is the gross profit percentage desired, then:

M = 1/(1-G)