What "spare money only" really means

"Invest only spare money." You've surely heard it countless times, and I've said it countless times. But saying it a lot, I noticed a problem: everyone nods, yet the moment it lands on themselves, their reading of "spare money" splits every which way. Some count the leftover in their paycheck account as spare money, some throw in the money set aside for next year's down payment, and some treat the entire credit limit they can swipe as "investable funds."

So in this piece I want to pry those two words apart and make them clear. It isn't a feeling; it's a number you can compute.

My own "spare money" illusion

When I got in back in 2021, I felt great about myself — I was using money that was "obviously all spare." The money in my account genuinely had nothing it needed to pay for right then. But I overlooked two things: I hadn't kept a big enough emergency fund, and part of that money was earmarked to be used six months later.

Then the 2022 drop arrived and my account got cut in half. As luck would have it, my family had an expense I couldn't dodge around that time, and I had to cut a portion off at a very low price for the emergency. That cut I still remember to this day — not because of how hard it had fallen, but because I shouldn't have been forced to sell at that moment at all.

Only later did I understand: what I'd invested wasn't spare money, it was "money temporarily not in use, but actually already claimed." Those two are worlds apart.

Spare money = total money − three things

The way I judge now whether money is spare money uses a very simple subtraction. From all the savings you can mobilize, first subtract these three things; only what's left counts:

• One, the emergency fund. Usually three to six months of living costs, set aside specifically for job loss, illness, or a sudden family expense. This money must be available at any time and can't fluctuate, so it absolutely cannot be invested. Why the emergency fund comes before investing, I wrote up separately: Before you get in, set aside your emergency money.
• Two, money with a clear use in the next year or two. Tuition, rent, a car, a down payment, a wedding — any money where you already know roughly when and how much you'll spend isn't spare money. Because crypto's down cycles can be long, and when you need the money you may well be stuck right at a low.
• Three, high-interest debt you owe. If you're still carrying credit-card installments, online loans, and the like, the "return" from putting money toward that debt is most likely steadier than your investing. Investing while carrying high-interest debt is like bailing water while a hole keeps leaking.

Subtract those three cleanly, and what's left — money you could leave untouched long-term, or even lose entirely, without disrupting your normal life — is the real spare money. Its core trait is just one thing: no deadline pressure.

A very simple self-check

If you can't tally those three cleanly for now, there's a faster self-check. Ask yourself one sentence:

If this money were locked away for three years untouchable, and after three years only two or three tenths were left, would my life fall into disorder?

Why do I use "three years" and "only two or three tenths left"? Because they roughly correspond to crypto's reality: a deep bear cycle can drag on a year or two or even longer, and after bitcoin's high of around $69,000 in November 2021, it at one point dropped to about $15,500 by November 2022, a fall of roughly 77% (public market records) — that is, "only two or three tenths left." If your life would fall into disorder under that worst-case assumption, then it isn't spare money, and you've invested too much.

A few common kinds of fake spare money

Here are the kinds of "money pretending to be spare money" I've seen most; check yourself against them:

• "Not in use right now" money. Not in use doesn't mean unclaimed. Next quarter's rent really is sitting in your account, but it already has an owner.
• Borrowed emergency fund. "Let me invest the emergency fund for a while and redeem it if something actually comes up" — but what if you need it urgently right when a deep drop hits? Once the emergency fund fluctuates, it's no longer an emergency fund.
• Borrowed money. Credit cards, online loans, money borrowed from people — this money has a cost and a deadline, which strips you outright of the ability to wait long-term. It's the most dangerous kind of fake spare money.
• "Pay it back once I win" money. Every "use it now, top it back up once I win" scheme is built on the illusion that "I will definitely win." When the market doesn't cooperate, this money forces you out at the worst possible moment.

Recap

To wrap up: spare money isn't "money not in use right now"; it's "money that, after subtracting the emergency fund, money needed in the next year or two, and debt, can sit untouched long-term and could be lost entirely without disrupting your life." A lot of what people call spare money confuses temporarily idle with truly free.

Once this spare-money line is drawn clearly, "how much to invest" starts to mean something — after all, every dollar you invest has to be spare money first. Once you've worked out how much spare money you have, the next step is figuring out how much of it should actually go into crypto, which I cover in more detail in How much should you put into crypto.