NPV?

By table, I'm guessing you're referring to the discount rates?

As you know, NPV = (Sum of (cashflows year t) * (discount rate year t) from year t = 1 to N ) + Initial investment

The discount rates are 1 / (1 + discount rate )^t

The table is just a look-up table for those discount rates. On one axis you have years/time periods, on the other discount rate.

Let's say you have the following data:

Initial investment = -20

CF(t=1) = 10

CF(t=2) = 20

CF(t=3) = 30

And with different discount rates

r(t=1,2,3) = 5%

Your NPV is then

NPV = CF(t=1) x r(t=1)+CF(t=2) x r(t=2)+CF(t=3) x r(t=3)-Investment

From the lookup table (for example this link) you find the following:

Period 1, Discount Rate 5% : 0.9524

Period 2, DR 5% : 0.9070

Period 3, DR 5%: 0.8638

Ok, now you can insert all the data into your NPV equation

NPV = CF(t=1) x r(t=1)+CF(t=2) x r(t=2)+CF(t=3) x r(t=3)-Investment NPV = (10)x(0.9524)+(20)x(0.9070)+(30)x(0.8638)-20 = 33.575

If the yearly rates are different (year 1, i = 5%, year 2, i =3%, etc.), you simply multiply the discount rates, instead of using the table.

i.e

CF(1) * 1/(1+r1) + CF(2) * 1/((1+r1)(1+r2)) + ... + CF(N) * 1/((1+r1)(1+r2)...(1+rN))

.