Investing a lump sum now versus spreading it as monthly contributions.
Lump sum advantage
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Lump sum value
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Phased value
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The question this settles
You have just come into a sum of money. A bonus, an inheritance, the proceeds of a property sale, a maturing endowment. The instinct of many South African investors is to drip it into the market over a year or two, because putting it all in at once feels like tempting fate. This tool puts a number on that instinct. It compares investing the whole amount today against spreading the identical total as equal monthly deposits, then grows each path for the rest of your horizon at the same return, so you can see what the caution actually costs.
The mechanics matter. The lump sum compounds for the full term from day one. The phased version splits the money into equal monthly slices, and each slice only starts compounding when it is deposited, so the last slice has the least time to grow. Because every rand in the lump sum spends longer in the market, and a steady positive return rewards time, the lump sum will almost always finish ahead in this model.
A R600,000 windfall over ten years
The calculator loads with R600,000 to invest, an 11 percent annual return, a ten-year horizon, and a choice to spread the money over the first 12 months. Phasing in means investing R50,000 a month for a year, then letting everything ride to year ten. Here is how the two routes land.
| Path | Value at year 10 |
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So phasing in over a single year costs roughly R78,800 of final value on this R600,000, using the return this calculator applies. That is the price of the comfort. Notice it is real money, close to 13 percent of the starting amount, yet it is far from catastrophic, which is the honest tension at the centre of this decision.
Why the textbook answer has an asterisk
This model assumes a smooth, constant return. Real markets do not deliver that. They lurch, and the order of good and bad years is unknowable in advance. If a sharp drop arrives in month two, the lump-sum investor wears the full fall while the phased investor still has most of the cash on the sidelines, buying in cheaper. Over long histories the lump sum wins most of the time, because markets rise more often than they fall, but the phasing strategy genuinely lowers the worst-case regret. The tool measures expected value, not the knot in your stomach.
There is also a behavioural truth worth naming. The best strategy is the one you will actually follow. An investor who commits the whole sum and then panics out after a 20 percent dip has done far worse than one who phased in and stayed the course. If spreading the money is what keeps you invested, the modest cost shown here can be money well spent.
Is this the same as rand-cost averaging into a fund I already buy monthly?
No, and the distinction trips people up. Rand-cost averaging from your salary is simply investing as you earn, because the money was never available all at once. This tool is about a sum you already hold today. Deliberately holding cash to drip it in is a timing decision, and that is the choice being measured, not your ordinary monthly debit order.
Does tax change which option wins?
The growth itself is taxed the same way regardless of how you entered, but where you hold it matters more than the entry method. Inside a tax-free savings account, growth and withdrawals escape tax entirely, though SARS caps contributions at R36,000 a year and R500,000 over your lifetime, with a 40 percent penalty on excess, so a large lump sum cannot all go in at once. In a taxable account, capital gains tax applies on disposal, with 40 percent of the gain above the annual exclusion included in your income. Confirm the current limits and exclusion with SARS, because phasing a big windfall is sometimes forced by the annual contribution cap rather than chosen.