i think that's not correct. he's calculating by monthly basis.

i forgot my maths formula is secondary school  but what he means should be

Month1 : 5000 x 0.031 + 5000 = 5155
Month2 : 5155 x 0.031 + 5155 = 5314.81
Month3 : 5314.81 x 0.031 + 5314.81 = 5479.56
and so on... anyone knows what kind of formula is this again?

BTW where do you get 3.1% interest per MONTH?? I'm also VERY interested. Most banks gives such interest by YEARLY basis, so you need to divide 12 again oh..

for me i calculate like this ..

3.1% / 12 (1 year) = 1 (month) = 0.258%

1st month    5000    + 0.258% = 5012.9
2nd month  5012.9 + 0.258% = 5025.8
.
.
.
24th month  = 5319.39

just use normal calculator

TS want to compound to 20 years (240 months)
Let's assuming 1 year has 365 days
What is the formula to count compounding interest for 7300 days?