VittVishesh has simplified how much of tax you can actually save by using TAX saving instruments under section 80C and NPS additional contribution. Based on your taxable income you can get a fair idea in percentage that how much of your 80C+NPS investment is saving you on gross without any exemption tax amount and percentage of tax saved with amount invested in 80C+NPS.
You need to input your Gross CTC + tax exempt deductions in yellow cells. You will get the simplified calculations. Tax calculation Option B provides a drop down to select percentage of 80C or NPS contribution which you intend to plan for tax saving. This simplified calculator will give descent decision support on how much of investment you should do in current financial year (2017-18). You can test several what-if combinations of Taxable income and tax saving amounts