All of our guidelines are in place to avoid quality issues, and ensure we can provide you with a final product that meets our high standards.
Because both printing and trimming processes are variable within some margin of machine error, there is always some chance that the paper will be cut too far in, cutting away an important part of the content. This is why it is important to keep your text and important images within the recommended safety margins.
Safety margin zones range from 0.125" (1/8") to 0.25" (1/4") depending on the paperstock and output method (digital or offset). Most products require 0.125" for the safety margin. For a list of products that require the larger 0.25" safety margin, see: Larger Safety Margin Required.
As a designer, using a wider safety margin (0.25") will preserve the integrity of your design no matter which paperstock you print.
The attached screenshot shows how to define the Bleed and Safety Margin in InDesign:
You cannot define a safety margin in Photoshop or Illustrator - If you are using either of these programs you will need to use guides in the document.
Create a document that's 0.25" wider and 0.25" higher than the print product you are ordering. A business card is 3.5 x 2" so your document needs to be 3.75 x 2.25". Place the guidelines for the safety margin 0.25" (for regular paperstocks) and 0.375" (for thicker paperstocks) away from the edges of your document - that's 0.125" respectively 0.25" away from the trim line.
(the guidelines for the bleed need to be set 0.125" away from the edges of your document).
You can define bleed in Illustrator, so your document needs to have the size of the ordered product - for a business card 3.5" x 2" - and the bleed defined as 0.125". Once you create the document you need to turn on the rulers (View-> Rulers-> Show Rulers) and click-drag it onto the canvas to create a guide. Place the guides 0.125" (for regular paperstocks) and 0.25" (for thicker paperstocks) away from the edge of the artboard.