Just an added bonus for those of you who wanna maximize everything to the extreme, given now that we can open so many 5% jars.

We already know that the first 36.60 MYR will earn the effective 10% p.a. interest.

I said earlier that anything above 36.60 will earn 5% p.a., but that's not entirely correct.

The next (and subsequent) 0.01 MYR interest crediting (above the original 0.01 MYR on the 36.60 principal) will only occur when the interests are 0.015, 0.025, 0.035, 0.045 etc.

Let's do some checking:

1. (0.005/0.05)*366 = 36.60
2. (0.015/0.05)*366 = 109.80
3. (0.025/0.05)*366 = 183
4. (0.035/0.05)*366 = 256.20

and so on.

Notice the difference between the consecutive cases (4-3, 3-2, 2-1) are all by the exact same amount 73.20 MYR. It makes sense because the marginal interest rate is 5% p.a., and so 73.20 MYR * 0.05 / 366 = 0.01 MYR (this is where the extra 0.01 comes from on top of the original 36.60 MYR).

If your deposit amount is between the numbers (e.g. 109.80 > 5% jar amount > 36.60, 183 > 5% jar amount > 109.80, etc.), you will only earn up to the previous case's interest.

E.g. if you deposit 50 MYR, you earn case 1's interest of 0.01 MYR (this is as if you deposited only 36.60 MYR).

So if you want to fully utilize your money, make sure you arrange your deposits such that it hits exactly the number 36.60, 109.80, 183, 256.20 etc. Anything in between is deemed "inefficient".

You can obtain the "cases" by applying the formula (0.005+n*0.01)/0.05*366 where n = 0, 1, 2, 3, ... (For the mathematically-inclined, the number sequence forms an arithmetic progression with starting value, a = 36.60 and common difference, d = 73.20, T_n = a + (n-1)*d, n = 1,2,3,...)

My birthday jar money automatically withdrawn to DSA, but missing the interest for 31st October