The Passive House Planning Package (PHPP) is the most effective way to plan and design energy efficient buildings and retrofits. The energy balance and planning tool is easy to use and provides reliable calculations, as has already been experienced by several thousand users. There are now a number of 3rd party tools and plugins available to ensure you achieve your energy efficiency targets.
Check out this blog post via the International Passive House Association website: https://blog.passivehouse-international.org/essential-tools-plugins-addons-for-phpp/