Every other lesson in this path is about how. This one is about how much — the question most people skip, and the one that decides whether crypto becomes an interesting part of your finances or a genuinely bad year.
There is no correct percentage. Anyone who gives you one without knowing your circumstances is guessing. What there is, is a test you can apply to any number you are considering.
The only test that matters
Take the amount you are thinking of putting in. Now assume it falls by 70% and stays there for two years. Not as a worst case — as an ordinary one. Could you still pay your rent, your bills and your insurance? And more importantly: would you leave it alone, or would you sell?
If the honest answer is that you would sell, the amount is too big. That is not a judgement about the coin. It is that a plan you abandon at the worst possible moment is the most reliable way to turn ordinary volatility into permanent loss — you lock in the fall, and you are out of the market for whatever comes next.
Working out your own number
Most people get to a sensible answer from the bottom up rather than the top down. First an emergency fund that has nothing to do with crypto — the months of expenses you would need if your income stopped tomorrow. Then any debt costing you more in interest than a realistic return. Then money already earmarked for something specific and dated: a house deposit, a wedding, a car. Whatever remains after those is the pool you can consider investing at all, and crypto is one candidate among several for a slice of it.
Two rules survive contact with reality. Never borrow to buy it — leverage turns an ordinary fall into a forced sale. And never invest money whose absence would change how you live. Crypto trades 24 hours a day and moves fastest when you are least able to think clearly, which is exactly why the size question is settled in advance rather than in the moment.
None of this is personal financial advice — we do not know your income, your debts or your goals, and the right answer genuinely differs between two people looking at the same chart. If the amount is large enough to matter to your future, that is the point at which a licensed financial adviser earns their fee. What this lesson can tell you is that the size decision deserves more of your attention than the choice of coin, and it almost never gets it.
🎯 Key takeaways
- There is no correct percentage — only an amount you could hold through a 70% fall without selling.
- In our records since mid-2025, Bitcoin fell 55% from its peak and Ethereum 70%. Smaller coins fell further.
- Emergency fund, expensive debt and dated goals come first; crypto competes for whatever is left.
- Never borrow to buy, and never invest money whose absence would change how you live.
- Decide the size before you open the app, not while the price is moving.
Educational content only, not financial advice.