The Calculator will work equally well with Lump Sums, as it will with regular savings or a combination of both.
The difference, however, is that regular savings benefit from an effect called 'pound cost averaging', which works on the basis that it doesn't matter if the value of investment units falls since you will then buy more units that month than you would if the price had risen. Over a longer term, this effect actually improves the investment return as long as the unit cost finishes at the same level or higher than it was when you started saving, which is normally the case.
Lump sums investments in the longer term options such as OEICs and Unit and Investment trusts do not benefit from this averaging effect; your money is invested more in a 'roller coaster' environment and goes up or down according to market movements. Over the longer term, these movements also average the return but in a different way; the more different shares involved the greater the effect as even when most share prices are falling, some will be rising, introducing a spread of risk. It is for this reason that investment in this type of plan should not be attempted for short term gains - the shorter the term, the higher the risk involved.
Nevertheless, historically at least, the return on this type of investment is normally higher than it is with cash deposit accounts. Reward and Risk are investment twins; you don't get one without the other.
