Magnetic helicity is the fundamental property that governs the structure and evolution of CMEs. While it is approximately a conserved quantity in a closed system, even with magnetic reconnection, it can transform between self and mutual helicities and within self-helicity, between twist and writhe. CMEs, when measured in situ, are often described as highly twisted magnetic flux ropes with all other forms of magnetic helicity being neglected. It has been a challenge to apply mathematical formalism and techniques developed to quantify and visualize the magnetic helicity of active regions and filaments to CMEs when they are simulated or measured in the interplanetary space. Here, we present results from our recent efforts to visualize and quantify the magnetic helicity of CMEs at 1 AU, starting from 3-D magneto-hydrodynamical (MHD) simulations. We find that neglecting mutual helicity and writhe, as is commonly done, may result in a significant under- or over-estimation of the CME magnetic helicity when it reaches 1 AU and therefore mis-assess their structure.