How to calculate savings interest

I'm sure many people out there don't know how the interest is calculated. They are contented so long they see the amount is roughly correct.

Below is taken from the UOB website as at 2017-10-18:

Many may be fooled by the 3.33% p.a. rate at first sight as the actual effective rate is only 2.43% p.a. if you fulfil the spending and crediting criteria.

Effective rate for 50k = (10k * 1.5% + 20k * 2% + 20k * 3.33%) / 50k = 2.43% which is shown in the fine print at the bottom of the page.

How to calculate the monthly interest?

Monthly interest = Effective interest rate * savings amount * (N / Y) where N is the number of days in the month. Y is the number of days in the year.

There may be some rounding differences.

The savings amount may be the daily average balance in the month depending on the definition used by the bank.