jakecubee wrote:
I was just wondering, how much intrest per day would you have to get so everytime, the intrest goes up?
Interesting question. Let's see.
The Neopets interest equation goes like this:
d = (i x P) / 365
where d is the daily interest, i is the current interest rate, P is the principle, and 365 is the assumed number of days per year. We can also write this as:
d = (i / 365) (P)
For the interest to change every day, assuming the interest rate remained the same, you want:
d2 - d1 = 1
where d2 is the daily interest for a given day and d1 was the daily interest for the day before. 1 is the minimum possible increase in daily interest, since Neopets doesn't use decimals, so we want to check when the change in daily interest caused by d1 to be at least 1.
d2 = (i / 365) (P + d1), and
d1 = (i / 365) (P)
so,
d2 - d1 = 1 becomes
[(i / 365) (P + d1)] - [(i / 365) (P)] = 1, or, factoring out the (i / 365),
(i / 365) (P + d1 - P) = 1, simplifying,
(i / 365) (d1) = 1
Isolating d1,
d1 = 1 / (i / 365), or
d1 = 365 / i
So, if your current interest rate is 10.5%, it is calculated as follows:
d1 = 365 / 10.5% = 365 / 0.105 = 3,476.19 or rounded up 3,477
In other words, if your current interest rate is 10.5%, your daily interest would have to be at least 3,477 NP to cause the next day's daily interest to be at least 1 NP more. But, if your principle is large enough to get that much daily interest, your account should be eligible for an interest rate higher than 10.5%.