How can I calculate EMI mentally in my head? How can I calculate the EMI mentally?
For example - 2 million  is the loan amount.  The ROI per annum is 12% and the tenure is 20 years.
What I can make out is the following -
ROI per month is 12/12* 100 i.e. 0.01
Now, tenure is 20 years or 20 * 12 months i.e. 240 months.
So, EMI has to be distributed in 240 months.
Now, according to the links -
the formula is
EMI = [P x R x (1+R)N]/[(1+R)N-1],
However, I am not sure how I can solve this mentally.
 A: Here's a mental math approach that will give you a back-of-the-envelope estimate.
The big problem, of course, is estimating (1 + r)n mentally.
We can make quick work of this with the rule of 72. The standard version states that the number 72 divided by an annual interest rate gives the number of years it takes your investment to double at that interest rate.
By the same math, it can also be used to approximate how long before (1 + r)n becomes 2.
Similarly, the rule of 114 helps determine how long it takes (1 + r)n becomes 3, and the rule of 144 helps determine how long it takes (1 + r)n to become 4.
At 12%, the (1 + r)n would reach 2 in about 6 years (72 ÷ 12 = 6), 3 in 9.5 years (114 ÷ 12 = 9.5), and 4 in 12 years (144 ÷ 12 = 12).
Hmmm...that 9.5 years to reach 3 is an interesting number, as it's just under half of 20 years. Let's see...if (1 + r)n becomes 3 after about 9.5 years, then in 19 years, it's going to be 3 times 3, or 9!
1 more year (to make 20) means another 12% on top of that, so 9 * 1.12 = 10.08. So, we can estimate that (1 + 0.12)20, or (1 + 0.01)240 for that matter, is going to be about 10.
Let's call this number x. So, in this example, x = 10
The next steps are relatively simple:
Subtract 1 from x. (x - 1)
Turn the number into its reciprocal. (1/(x - 1))
Add 1. ( 1 + (1/(x - 1)))
Multiply this amount by the MONTHLY interest rate. ( 1 + (1/(x - 1))) × r
Multiply this amount by the principal, and you have a rough idea of your equated monthly installment! ( 1 + (1/(x - 1))) × r × p
As an example, let's work through this with 10:
Subtract 1: 10 - 1 = 9
Reciprocal: 1/9 (about 1.11)
Multiply by monthly interest rate: 1.11 × 0.01 = 0.0111
Multiply this by the principal: 0.0111 × 2000000 ≈ 22200
So, the EMI should be somewhere around $22,200.
Wolfram|Alpha puts the exact amount at $22,022. Not bad for a mental estimate!
