Natwest Savings Builder

greengrass1

Provided at least £100 is paid into this account each month and no money is ever removed should the interest paid always be more than the previous month if the interest rate remains the same???

Or are there issues with different months not having as many days etc.

eskbanker

No - according to http://personal.natwest.com/personal/savings/savings-builder.html:

Interest is calculated daily and paid on the first business day of the month

so, since there have been 29 days between the first business day of July (Monday 3rd) and the first business day of August (Tuesday 1st), compared with 32 days between 1 June and 3 July, this month's interest would be circa 10% lower than last month's on the same balance, although the effect of the additional deposits during the month would cancel some of this out....

There are also the tiered rates (shown on that same linked page) so if you cross a threshold from one band to another then this will affect your interest.

Eastminster

Please also pay close attention to the second-last business day monthly funding requirement which has caught out many people.

The basic interest for £1 to £5,000 is 0.10% which increases to 1.50% if the bonus condition is met. The terms read as follows.

Bonus Condition
How do I earn bonus interest?
To earn the bonus in each monthly bonus period, your balance must grow by at
least £100.
A monthly bonus period runs from close of business on the second-last business
day of one month, to close of business on the second-last business day of the
following month.
Close of business times depend on whether you pay in your money in-branch or
by using our telephone, online or mobile banking services.

It is somewhat convoluted but has the advantage over all other regular saver that a lump sum of several thousand pounds can be deposited on day 1.