The web version will never be as fast as the desktop version due to the remote nature of a web based application and the data communication. With a reasonably high speed internet connection (15 MBs or more), users should experience acceptable performance. We are working to further optimize the speed and performance and will be rolling out updates periodically to further improve the speed.
Additionally, the offline version (constant internet access not needed) will not require data transfer via the internet. If you have a slow internet connection this will improve the user experience.
Here are instructions to install the Offline Mode: https://p.widencdn.net/wbl8xk/BC-Calc-Offline-Mode-Setup