Low interest rates might be great news for borrowers but they can have a devastating effect on savers' long-term wealth. Furthermore, with inflation tending to run in excess of interest rates, the buying power of money is being eroded, even though the value of capital might appear safe. Therefore, it is important to keep a close eye on the interest that is being earned.

Nowhere is this more apparent than with cash Individual Savings Accounts (ISAs). According to Moneyfacts, the average long-term fixed-rate cash ISA offered a rate of 2.27% at the start of August 2014, compared with 3.58% in April 2012.

It is good practice to retain some cash in an easy-access deposit account to ensure unforeseen emergencies and short-term necessities can be funded. However, there is no reason to tie up all your cash holdings in this type of account. Research by Skipton Building Society, for example, found more than 75% of pensioners with an ISA never withdraw money from their account, and interest rates can be significantly higher for those willing to sacrifice some flexibility.

Life is hectic and it is all too easy to forget about your ISAs until the end of the tax year is looming. Rather than waiting until the eleventh hour, however, take the time to shop around now for the best possible home for your money. This may be easier to remember this year since the introduction of NISAs - the 'New ISA' in July.

The 'New ISA' limit is £15,000 and can be invested in cash, stocks & shares or a combination of the two. Investors will also be able to transfer ISA savings from previous years freely between stocks & shares and cash.

Moreover, any interest on cash held within a stocks & shares NISA is free of tax. This means that there is only the need to hold one NISA, rather than separate NISAs for cash and stocks & shares. This simplicity might be attractive to some investors although, you should not assume you will receive the best rate of interest on the cash element, and it might be worth having a separate cash NISA if you want a competitive rate. You can also transfer your NISAs freely between providers - subject to any penalties that might be applied by your existing provider - but you can only have one cash NISA and one stocks & shares NISA in any single tax year.

Any ISA subscription made between 6 April and 30 June 2014 will be counted against the £15,000 NISA subscription and you will not be allowed to open up a new NISA for the current tax year from 1 July. Instead, you will have to top up the existing account. Do check with your provider's terms and conditions - particularly if you have already opened a fixed-rate cash ISA.

The range of investments that can be held within a NISA is also expanding - for example, investors will be able to hold corporate bonds with less than five years left to maturity. This expansion is likely to lead to an increase in new products from providers that, in turn, will provide greater choice for savers. One thing will not change, however - once it's gone, it's gone. At the end of each tax year, you lose any unused ISA allowance, so make sure you act in good time and, if you are unsure about anything, do seek professional advice.