Investing a fixed amount every month: does it actually work?
What regular investing does and does not achieve, why it suits most salaried investors, and how to set it up on PSX without an automatic mechanism.
Investing a fixed amount at regular intervals (often called a systematic investment plan, or simply rupee-cost averaging) is the approach that suits most salaried people. It is also frequently oversold, so it is worth being precise about what it does.
What it actually does
When you invest a fixed rupee amount regularly, you automatically buy more shares when prices are low and fewer when prices are high. Over time your average purchase price ends up below the average price over the period.
That is a real, arithmetic benefit. It is also a modest one, and it is not the main reason to do it.
The real reason it works
It removes the decision.
The largest destroyer of retail returns is not poor stock selection. It is behaviour, buying after a long rise because it feels safe, and refusing to buy after a fall because it feels dangerous. Both instincts are backwards, and both are extremely strong.
A fixed schedule takes the decision out of your hands at exactly the moments your judgement is least reliable. That is worth far more than the averaging arithmetic.
What it does not do
- It does not protect you from loss. If you invest regularly into a business that deteriorates permanently, you simply buy more of something falling.
- It does not beat investing a lump sum on average, if you happen to have the lump sum. Markets rise more often than they fall, so earlier money usually has more time to work.
- It does not remove the need to choose what to buy. Averaging into a bad decision does not improve it.
The second point deserves emphasis, because it is often glossed over. Regular investing is optimal for someone earning a salary and investing as the money arrives, which is most people. It is not automatically optimal for someone sitting on cash.
Setting it up on PSX
There is no automatic mechanism for individual shares of the kind mutual fund investors are used to. You do it manually, which means the structure has to survive your own inconsistency.
- Pick a fixed amount you can sustain in a bad month, not a good one. Consistency matters more than size.
- Pick a fixed date, tied to when your salary arrives.
- Set a recurring reminder. This is the entire enforcement mechanism, so do not skip it.
- Decide in advance what you are buying, either topping up existing holdings toward their target weights, or a set rotation.
- Check the cost per trade against your monthly amount. If fixed charges are eating a meaningful share, invest quarterly in larger amounts instead.
The rule that matters most
Do not stop when the market falls. That is the only time this strategy has a real advantage, and it is precisely when almost everyone abandons it.
If you find yourself wanting to pause during a decline, the honest reading is usually that the amount is too large for your comfort. Reduce it to a level you will maintain through a bad year, and keep going.
Investing Sparkle
We teach Pakistani investors to understand PSX and manage their own money. We do not hold client funds, execute trades, or recommend specific stocks.
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