How Much Should I Invest Every Month?

You will find advice to invest a fixed share of income, and as a rough orientation it is fine. As an answer it ignores everything that decides the question.

Two people on the same salary can have entirely different correct amounts: one with a loan running, three dependants and no buffer, the other with none of those. The rule treats them identically and they are not remotely in the same position.

It also ignores stage. Somebody at the start of a career and somebody a decade from retirement are solving different problems with the same monthly decision. Use a percentage as a sanity check on a number you derived some other way, not as the source of it.

Three things, and if any of them is missing the investing amount is not the question yet.

Expensive debt. A card balance or personal loan running alongside an investment is the wrong order, since clearing it has a certain outcome and nothing you invest in does.

A buffer. Without one, the first ordinary emergency becomes a redemption at whatever price is available that week, as our page on building an emergency fund sets out.

Fixed obligations. Rent, fees, household costs, anything committed. What is left after those is the pool the answer comes from.

Households that skip these and start with an ambitious instalment usually stop within a year, which is why we go through them first even when somebody came asking about schemes.

Where the money has a purpose and a date, the amount can be derived rather than guessed, and this is the more useful method.

Take the goal, the date, and what you already hold towards it, and the required contribution follows from arithmetic. Our goal SIP calculator does that on assumptions you supply, and our pages on child education and retirement cover the two commonest.

Two cautions. The figure depends on an assumed rate, which nobody knows, so treat it as an order of magnitude rather than a target. And if the required amount is larger than you can sustain, the answer is not to strain for it. It is to start with what you can hold, raise it as income grows, and revisit the goal, which our page on the step-up SIP covers.

Many households are investing simply because the money should not sit idle, and that is a perfectly good reason.

Here the method is different. Look at what actually remained unspent over the last several months, not what you think should remain, and start below that figure rather than at it. The gap between intended surplus and actual surplus is where most abandoned instalments come from.

One practical arrangement helps more than any calculation: set the date shortly after income arrives rather than at the end of the month. Money that leaves first tends not to be missed, and money left to the end tends not to be there.

Take your candidate figure and ask one question about it. Would you still pay this in a month where the car needed repairing and somebody had a medical bill?

If the honest answer is no, the number is too high, however comfortable it looks in an ordinary month. Difficult months are not rare events; they arrive several times a decade, and an instalment that only works in good ones is an instalment with an expiry date.

We would rather set an amount somebody keeps for eight years than a larger one they stop in year two, and we say so even though the second earns us more in the short run. Our post on restarting a SIP you stopped exists because the second outcome is so common.

Many households asking this question have both: a monthly capacity and an accumulated balance doing nothing in particular.

They are separate decisions and combining them produces a worse answer to both. The monthly figure should be set by what your income can sustain. The existing balance should be placed according to when you might need it, which our page on mutual funds versus a savings account works through.

Where the balance is going into one holding rather than several, a multi asset scheme is one arrangement households use, since it spreads and rebalances internally without further decisions.

What we would specifically avoid is using a lump sum to justify a monthly instalment larger than your income supports, on the basis that the balance can cover a difficult month. It can, once, and then the buffer is gone and the instalment is still too large.

Where the balance is substantial, moving it in gradually rather than at once is worth considering, as our page on lumpsum investment covers. That is a different question from how much per month.

Whatever you start with is not meant to be permanent, and the direction matters.

• Raise it when income rises, ideally on a set schedule rather than when you remember. This does more than any other adjustment available.
• Raise it when an obligation ends, such as a loan finishing, since the household is already used to living without that money.
• Reduce rather than stop when things are tight, because a reduced instalment can be raised again and a stopped one frequently is not.

What we would not do is set the figure once and leave it for fifteen years. A fixed amount quietly shrinks against a growing income, and that is the commonest slow failure we see in otherwise well-run households. To work out a number you can actually hold to, get in touch.