How Many Shares Should You Hold in the Challenge?

Why the number of shares matters

Your £100,000 is finite. The way you divide it is your first strategic decision of the challenge, and it has consequences that run all the way to the final league table. More shares mean more diversification — your results become smoother because no single company can swing your whole portfolio dramatically. Fewer shares mean more concentration — higher highs are possible, but so are lower lows.

There is also a practical wrinkle specific to this challenge: the Windfall Tax discourages frequent changes to your portfolio, so your initial spread matters more than it might in a free-trading scenario. Getting the balance right at the start means you do not have to keep reshuffling under a financial penalty.

Concentration risk — what happens when you put too much in one place

Concentration risk is the danger that comes from having too large a portion of your portfolio in one share or one sector. A worked example makes this concrete.

Suppose you put £50,000 (half your portfolio) into a single company. If that company’s share price falls 20% in a bad week, you have lost £10,000 — a tenth of your entire portfolio, from one decision. Now compare that to a ten-share portfolio where each holding is worth roughly £10,000. The same 20% fall in one share costs you £2,000 — painful, but manageable. The rest of your portfolio carries on.

There is a less obvious version of concentration risk worth knowing about: whole-sector concentration. If you buy five energy companies, or three banks, or four housebuilders, you might think you are diversified because you hold multiple shares. But one macro event — an oil price swing, a rate change, a regulatory announcement — can hit every one of those companies at the same time. You have concentrated risk at the sector level even if your individual positions look spread out.

What “too many” looks like

There is a limit to how much diversification actually helps you, and beyond that limit it starts to hurt. Owning 20 or 30 shares does not make your portfolio 20 or 30 times better researched — it usually just means you understand each one less.

The challenge runs for months. Over that time, companies report results, issue trading updates, warn on profits, or get caught up in sector-wide news. You need to be able to notice when something important happens to each company you own and have a view on what it means for your holding. A portfolio you genuinely understand will almost always beat one that is technically “diversified” but chosen at random and then ignored.

If you find yourself unable to explain in a sentence why you own one of your shares, that is a sign your portfolio is already too spread out to manage well.

The Active and Strategic portfolios need different thinking

One of the most important features of the challenge is the two-portfolio structure, and it changes how you should think about concentration. If you want the full picture on how the two portfolios work, read the dedicated article on the Active and Strategic portfolios.

The short version for this discussion:

• Active portfolio: You can trade throughout round one, which gives you scope to rotate out of a share that goes wrong and into a better opportunity. A slightly tighter concentration — around 8–10 shares — keeps your decisions manageable and means each trade is meaningful.
• Strategic portfolio: This is a buy-and-hold structure. Your picks need to weather the full round largely on their own, because selling to cut a loss triggers the Windfall Tax on any gains you have elsewhere. A little more spread helps here — 8–12 shares, deliberately spread across different sectors — because you cannot adjust easily without a cost.

The combined score rewards both portfolios performing well. Piling all your conviction into one and scattering the other wastes the structure the challenge gives you. Think of them as two separate tasks: one where you can be a bit more active, and one where discipline and initial research do the work.

A practical starting point: the 8–12 rule

Most experienced participants settle somewhere in the 8–12 share range for round one. This is not a magic number — it is a range that tends to balance three competing demands: enough diversification to contain disasters, enough concentration to beat the market, and enough simplicity to actually track what you own.

Position sizing — equal weight or conviction weight?

Once you have decided how many shares to hold, you need to decide how much of your £100,000 to put into each one. Two approaches are common:

Equal weighting means dividing your money roughly evenly: if you hold ten shares, each gets around £10,000. This is simpler to track and keeps any single mistake bounded. If one share falls sharply, the damage is roughly the same regardless of which share it was.

Conviction weighting means putting more money behind your highest-confidence ideas. If you are particularly sure about a company after doing thorough research, you might put £15,000 there and less elsewhere. This can work — but only if that conviction genuinely comes from research. The risk is that strong convictions are sometimes just strong biases. A company that you like the sound of is not the same as a company with solid fundamentals and a clear growth story. For most participants starting round one, equal weighting is the safer default.

Sector spread

Aim to have at least four or five different sectors represented in your portfolio. The FTSE 100 includes sectors such as financials, energy, consumer staples, industrials, healthcare, utilities, technology, and materials — a guide to these is in the article on stock market sectors.

Spreading across sectors protects you when a single macro event dominates the news cycle. An oil price spike is great for energy shares and terrible for airlines. A rate hike affects banks differently from housebuilders. If you are spread across sectors, one of those stories helps you even as another hurts you. That is diversification doing its job.

MoneyHelper, the UK government’s financial guidance service, has a clear introduction to why spreading risk across asset types and sectors matters: Understanding investment risk — MoneyHelper.

How your share count affects your rank

Concentrated portfolios have higher variance. Statistically, a portfolio of three shares is more likely to sit near the very top of the league table — and just as likely to sit near the very bottom. This is not random luck; it is a direct consequence of putting a lot of weight on a small number of bets.

If your goal is to reach the semi-finals from a field of thousands of teams, a moderate spread gives you a more reliable path than a binary bet on two or three stocks. You do not need to be in the top 1% — you need to be in the top 15–20%. A steadier portfolio with good sector coverage and solid individual stock research is usually the better vehicle for that goal.

That said, if you are already in a comfortable mid-round position and want to push higher, targeted concentration in your Active portfolio can be a deliberate late-round strategy: you take a higher-variance bet on a share you have researched carefully, knowing that the downside is that you stay roughly where you are. Understanding how the ranking and combined score work is key to judging when this trade-off makes sense — see how portfolio ranking works for the mechanics.

Three common mistakes to avoid

1. All-in on one theme. Piling into AI shares, or only buying housebuilders, or loading up entirely on oil majors. One macro turn and the whole portfolio moves the same way. The theme might be right, but the lack of any hedge means one bad piece of news is very hard to absorb.

2. Tiny positions you do not follow. Buying fifteen shares “just in case” and then ignoring half of them. The Windfall Tax means that cutting a loser is not free — if you have gains elsewhere, selling one share triggers a charge. So if you own a share you are not tracking, you may sit on a loser longer than you should, compounding the problem.

3. Copying the index too closely. A portfolio that holds twenty shares spread evenly across all FTSE 100 sectors is essentially tracking the market. It cannot beat the league because outperforming a passive benchmark is exactly what the challenge tests. You need some genuine views — and a spread tight enough to act on them.

A quick checklist before you finalise your picks

Before you lock in your round-one portfolio, run through these questions. If any answer is “no”, rethink that position:

• ☐ Can I explain in one sentence why I own each share?
• ☐ Are my shares spread across at least four different sectors?
• ☐ Does my total position sizing add up to roughly my full £100,000?
• ☐ Have I read recent results or a trading update for each company?
• ☐ Am I comfortable with how much any single share could affect my total?

If you are still building your research skills, the articles on how to research a share and picking your first shares cover the fundamentals of what to look at. The rules and portfolio structure page on the challenge site also explains exactly how the round is scored, which should inform your positioning before you commit.

FAQ

Is there a minimum or maximum number of shares I must hold in the Student Investor Challenge?

There is no set minimum or maximum. The platform lets you buy as many or as few London-listed shares as you like with your £100,000. Most competitive teams settle on 8–12 shares, which balances diversification with the ability to track and understand their picks.

Should I buy the same amount in every share?

Equal weighting is a good default, especially at the start of round one. It keeps any single mistake bounded and makes your performance easier to understand. Conviction weighting — putting more behind your top ideas — can work, but only if those ideas are backed by research rather than hype.

Can I add more shares later in round one, or am I stuck with my first picks?

You can trade in the Active portfolio throughout round one, so you can add or swap shares at any time. However, the Windfall Tax applies to gains you realise when you sell, so frequent switching eats into your combined score. The Strategic portfolio is designed to hold steady — treating it as buy-and-hold keeps the tax drag low.

What if two of my shares are in the same sector — is that always a problem?

Not always, but it adds risk. Owning two bank stocks is fine if you have a clear view on the sector. The issue is that two shares in the same sector will often rise and fall together, meaning you get less diversification benefit than it appears. Balance that against how strong your conviction is.