taxability of cumulative pension

Commuted pension received by government employees is wholly exempt from tax. 

In the case of commuted pension received by non-government employee, the maximum amount exempt from tax is restricted to the one-third of the total commuted pension, to which employee was entitled, where the employee also receives any gratuity.

Otherwise, the exemption is limited to commuted value of  50% of the pension to which employee is entitled.

Refer  are-pensions-taxable

&/or   tax-on-pension-income