After Buying in Batches, What Is Your Cost Basis Really?

You have bought the same coin three or four times. One day you open the account to work out whether you are up or down, and you find you cannot say: the holdings page shows one cost basis, the number you have been carrying in your head is another, and the two do not match. Push a little further and it gets murkier still. That green unrealized gain on the screen, how much of it would be left if you actually sold?

Here is the conclusion, and everything below is just that unpacked: your cost basis = everything you spent on these coins ÷ the number of units you hold now. The numerator includes the fees taken out of each buy; the denominator counts only what is still in your account. It is weighted by quantity, not the plain average of your buy prices.

Every number below is a made-up figure picked to make the arithmetic clear. None of it is a market quote or anybody's real fill. Fee rates differ between exchanges and can change at any time, so the rates here are assumptions used for the worked example; whatever the exchange page shows in real time is what counts.

Cost Basis Is Not the Average of Your Buy Prices

The most common way to get this wrong is to add up three buy prices and divide by three. That happens to be right in exactly one case: when every buy landed you the same number of units. And when you order by amount of money rather than by quantity, the units are never the same. A cheap week buys more, an expensive week buys less, and those differences have to count. The right way is to weight by quantity.

Say you bought the same coin three times, ordering by amount each time. All of the figures below are invented to keep the division easy and do not represent any real price:

You put in 6,500 and ended up with 40 units, so the cost basis is 6,500 ÷ 40 = 162.5. Averaging the three prices instead gives (200 + 100 + 250) ÷ 3 ≈ 183.3, more than twenty above the real number. The gap is the second buy: that was the lowest price, the same money bought twice as many units as the first time, so it deserves twice the say in the average.

One point that trips people up: if you sold part of the position along the way, take the sold units out of the denominator and take that share of the cost out of the numerator. Do not subtract the sale proceeds from your total money in. That version produces a strange cost basis and can even turn it negative.

Which Side Each Fee Belongs On

That 162.5 is still not the whole story, because the fee taken when you bought is real money you paid for these coins too. The rule is one line: buy fees go into the cost, sell fees come out of the gain. Neither side can be skipped, and putting one on the wrong side makes you either double-count it or lose it.

Carrying on with the example, assume a rate of 0.1% (purely an assumption chosen for easy arithmetic; follow whatever the exchange page shows in real time). The 6,500 of buying costs about 6.5 in fees, total money in becomes 6,506.5, and divided by 40 units the cost basis works out at about 162.7. That looks like small change, but this is only three buys. The more often you buy and the smaller each buy is, the more visible the stack becomes: a weekly schedule is fifty-odd orders a year, every one of them adding to the numerator.

To total them up at your own real rate, run the orders through the fee calculator one by one. For why rates come in tiers, what separates Maker from Taker and how to bring the rate down, see how trading fees work and how to pay less, which goes through it properly.

One more case to watch for: many exchanges let you pay fees with the platform coin. What gets deducted then is not the coin you bought but a different asset, which is easy to miss when you write the trade down. It is still cost, just in another shape.

Withdrawals and Cashing Out Eat Into It Too

Fees are only the most visible layer. Between your money leaving and the coin sitting in your account, and again between that and the money coming back to you, there are a few more places where value leaks out. Beginners tend to skip the whole line:

• The spread on the way in: turning your own currency into stablecoins with a card or through peer-to-peer trading usually gets you a slightly worse price than the mid-market rate at that moment. That difference never appears on a fee statement, but it is cost all the same.
• On-chain withdrawal fees: moving coins off an exchange into your own wallet costs a network fee, it varies a lot between chains, and it is charged per withdrawal, so the more you split it up the worse the deal.
• The way out: converting stablecoins back into your local currency carries a spread as well, and some channels add a charge on top.

Not all of these will land on you. If you simply bought and left the coins on the exchange for now, the only items on your side are the buy fee and the spread on the way in. But as soon as you plan to take the money back out one day, the return trip has a fare too, and plenty of people price only the outbound leg, which is why the final amount always comes in a little under expectations.

Paper Gain Versus What Actually Lands

The profit-and-loss figure on the holdings page is normally the current market price times the units you hold, minus the cost the exchange has on file. It is a number that has not happened yet, and there are several gates between it and money actually showing up in your bank account.

Keep going with the example. Say the price reaches 200 one day: 40 units are worth 8,000, minus 6,506.5 of money in leaves a paper gain of about 1,493. Turning that into money means getting past four things, in order: the fee taken when you sell; the price your sell order really fills at, which need not be the quote you were looking at, and least of all with a market order into a thin book; the spread on converting stablecoins back into your own currency; and whatever tax your jurisdiction applies to the gain (rules differ widely from place to place, follow your local ones, this page does not go into them).

So the question of how much you have made has two answers: a paper one and a realized one. Watching the paper figure day to day is fine, but when you are actually at the point of deciding whether to sell, redo the sum on the realized basis. For which prices and what pace suit selling in tranches, see when should you sell a bitcoin DCA, which gives three workable approaches.

Where Buying More Pulls Your Cost Basis

Once you can see that cost basis is weighted, the effect of buying more is easy to work out. In one line: a new buy pulls the cost basis toward its own price, and how far it pulls depends on how big that buy is next to the rest of the position.

Take the same 40 units at 162.5 (fees left out of this section to keep the main line visible). If the price falls to 100 and you spend another 4,000 on 40 more units, you hold 80 units with 10,500 in, and the cost basis drops to about 131. Same fall to 100, but you spend only 500 on 5 units: you hold 45 units with 7,000 in, and the cost basis drops only to about 155.6. To move the cost basis noticeably, a new buy has to be in the same order of magnitude as what you already hold. Buying in dribs and drabs barely moves it.

The other way round, if the price rises and you keep buying, the cost basis gets pulled up. There is nothing frightening about that: a higher cost basis does not mean you have lost anything, and the coins you hold are still worth the higher market price. The thing worth watching is something else. Plenty of people keep adding on the way down purely to pull the cost basis lower, and end up with far more money in than they ever planned to commit. Cost basis is a bookkeeping result, not a target to chase. Buying more so that the number looks better has nothing to do with why you bought the coin in the first place, and we would not recommend it: it leaves your position at its heaviest exactly when you are least sure of it.

If you are already buying a fixed amount on a fixed schedule, weighted cost is quietly doing this work for you; our piece what dollar-cost averaging is explains the mechanics. To see the rough shape of buying over a long stretch, put a few assumptions into the DCA return simulator, which is labeled for what it is: a hypothetical scenario, not a promise of returns.

Counting in USDT Is Not Counting in Your Own Currency

This is the one most often missed. If your pair is BTC/USDT, the cost basis the exchange works out for you is denominated in USDT. What you actually paid out, though, was your own currency, with a layer of exchange rate and spread in between at the point where you converted it into stablecoins.

The result is that the two sets of books can point in opposite directions: measured in USDT you are up, converted back into your own currency you are merely even, and it happens the other way round too. A stablecoin tracks the dollar, not your currency, so what it is worth to your purchasing power still carries an exchange-rate wobble. What stablecoins are covers what keeps them roughly steady, and what exactly they are steady against.

Choosing between them can be practical. If the money is eventually going back into your own currency to be spent, keep the books in your own currency and treat the amount you actually converted on the way in as the starting cost. If you plan to keep it circulating inside crypto for a long time, USDT is less work. Keeping both is fine as well, just do not read them mixed together, which is the fastest route to two conclusions that contradict each other.

The Fields Worth Writing Down on Every Trade

Exchanges keep your history, of course, but export formats differ from one to the next, and the moment you switch platforms or use two or three venues the records scatter. Keeping a light record of your own is much less trouble than digging through history afterwards.

Those are all the fields there should be. Any more and nobody keeps it up. The real enemy of record-keeping is not the arithmetic, it is the hassle, and it usually breaks in month three. How to sort what you hold into piles by purpose, and which pile to leave alone, is set out more fully in our piece you hold some crypto, now what.

When You Do Not Need This Much Precision

Having laid all that out, it is only fair to say where it is not worth the effort.

• When the total is small and you have bought once or twice. The cost basis the exchange shows is good enough for you, and time spent understanding what you actually bought pays better. For what to watch on your first order, see buying your first coin, which has the full steps.
• When you have no intention of selling. Cost basis earns its keep at two moments: deciding whether to buy more, and deciding whether to sell. Do neither and it is just a number that moves your mood, and you sleep better not looking at it.
• When the money underneath is not in place yet. Agonizing over cost basis before you have even a few months of spare cash is the wrong order. Where that belongs in the queue is spelled out in build your emergency fund before you enter crypto.

The value in this whole exercise is not getting the second decimal right. It is that working the number out forces you to write down two others: how much I have put in, and how much I hold now. The cost basis people carry by feel is usually a long way off the real one, and every judgement about whether to sell is built on it. For why these scattered small decimals turn into large numbers once you stretch the time out, get compounding and inflation straight is the companion lesson. Like a squirrel with its pine nuts: work out where each one is buried first, then talk about getting through the winter.

Read more notes first

This site keeps Binance referral links only in selected step-by-step guides. If you sign up and trade through one of our links, any benefit for you depends on the platform's current promotion, and it does not change what we write. We are an independent third-party information site, not the official Binance website. Every price, quantity, rate and profit-or-loss figure in this article is a hypothetical example used to explain how cost basis is calculated; none of it is a real fill and none of it is a promise of returns. Rates and processes follow whatever the exchange page shows in real time. Crypto prices swing hard and you can lose your entire stake. This is for education only and is not financial advice.