Since the new tax regime is the default tax regime, filing income tax return (ITR) under the old regime would require you to switch from the new tax regime. However, before you do that -- it is imperative to be aware of certain key rules which govern the switch.Notably, the rules with regards to switching of tax regime depend on the source of income of taxpayers: salary or business/ profession.Which tax regime to choose?Taxpayers can file tax return under the old tax regime if they believe that this would lead to some amount of tax saving. On the other hand, if filing tax return under the new tax regime is profitable then naturally, one would opt for the default regime.What rules apply to salaried employees?Salaried taxpayers can switch the tax regime from old to new and vice versa every year.There is no restriction on salaried employees with regards to switching between the two tax regimes as they can do it every year. However, the same flexibility is not available for persons wh...