Both Sprintax Returns and Sprintax Calculus are products owned by Sprintax, however they provided different services.
Sprintax Returns is a self-preparation software using which you can generate your Federal and State income tax returns as well as other forms such as form 8843, ITIN application forms and FICA claims. You can use Sprintax returns once the tax year is over and the tax offices have published their new regulations, typically starting from the end of January of the next calendar year. The deadline to file your tax returns is in general in April of the next calendar year after the tax year is over.
Sprintax Calculus is a software preparing pre-employment forms, which are often prepared during the tax year or before earning income. They can include forms such as W-4, W-8 BEN, W-9, form 8233 etc. If you will be earning income during the current calendar year and require help in how you can get correctly taxed, you can sign up for the Sprintax Calculus service.