Bought Crypto on Three Different Exchanges? Here's Why Your Real Cost Basis Is Probably Wrong
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6 min read
You bought Bitcoin on Indodax two years ago. Then you opened a Binance account for a coin Indodax doesn't list. Then a friend talked you into trying Pintu. Now you want one simple number: what did you actually pay for the Bitcoin you're holding? Open any one of those three apps and it will confidently give you an answer. It will also be wrong, because your crypto cost basis isn't sitting in any single app. It's split across three of them, and none can see the other two.
Cost basis is just what you paid for something, per unit. If you buy one share of a stock for Rp 10,000, your cost basis is Rp 10,000. Buy crypto in several purchases at different prices, and the useful number is the weighted average cost basis: add up everything you spent across every purchase, divide by the total amount you bought, and that single blended price is your real average cost per coin.
That math only works if it sees every purchase. Miss one, and the average it spits out isn't an approximation of the truth. It's a different number entirely.
Every exchange app, whether it's Indodax, Pintu or Binance, only knows about the trades that happened inside it. Indodax has no idea you also bought on Binance. Binance has never heard of your Pintu account. Each one calculates "your average cost" using only its own slice of your total position, then presents that partial number as if it were the whole picture.
This isn't a bug in any of these apps. They're doing exactly what they were built to do: tracking activity on their own platform. The gap only opens up because you, the investor, are the only one holding all three pieces, and most people never actually add them together by hand.
Here's how far off it can get, using real, dated Bitcoin prices rather than made-up ones. Say you bought 0.02 BTC on each of three exchanges, at three different points in time:
| Exchange | Date | Price per BTC | Quantity | Cost |
|---|---|---|---|---|
| Indodax | 21 Nov 2022 | $15,787 | 0.02 | $315.74 |
| Pintu | 24 Oct 2023 | $34,000 | 0.02 | $680.00 |
| Binance | 6 Aug 2026 | $64,510 | 0.02 | $1,290.20 |
| Total | 0.06 | $2,285.94 |
Those three prices are real historical closes, not estimates: $15,787 on 21 November 2022, Bitcoin's lowest close that month during the FTX collapse fallout (StatMuse Money, sourcing Yahoo Finance data, consistent with CNBC's reporting of the same week); $34,000 on 24 October 2023 (CNBC); and $64,510 on 6 August 2026 (Fortune, cross-referenced against CoinDesk). The 0.02 BTC per purchase is a round, made-up quantity chosen to keep the arithmetic simple.
Weighted average cost basis = Total amount spent ÷ Total quantity bought
Your true blended cost basis is $2,285.94 ÷ 0.06 = $38,099 per BTC. With Bitcoin trading around $78,750 on 26 August 2026 (Fortune, CoinDesk), your real gain across all 0.06 BTC is about 106.7%.
Now look at what each single app would have told you instead. Open only Binance, and it shows an average cost of $64,510, a gain of just 22.1% on the coins it can see, badly understating your real position. Open only Indodax, and it shows an average cost of $15,787, a gain of 398.7%, badly overstating it. Neither app is lying. Each is just answering a question ("what's my average cost on this exchange") that isn't the question you actually asked ("what's my average cost overall").
If you're worried a wrong cost basis means a wrong tax bill, there's good news: it doesn't, at least not in Indonesia. Since PMK 50/2025 took effect, crypto sales are taxed with a flat final rate on the gross transaction value, 0.21% on a licensed local platform, 1% on a foreign one, regardless of whether that specific sale made you money or lost you money. NetWort's own breakdown of the current crypto tax rates covers the full mechanics. Cost basis simply never enters that calculation.
What a wrong cost basis does cost you is your own judgment. If you think you're up 22% when you're actually up 107%, you might hold on far past your real comfort level with the risk. If you think you're up 399% when you're actually up 107%, you might sell early and give up real, still-compounding gains, or badly misjudge how much of your portfolio crypto has actually grown into. NetWort's look at crypto allocation drift after a rally walks through exactly this kind of decision, and it only works from a correct starting number.
The fix isn't switching exchanges or picking one app to trust. It's recording every purchase, no matter which exchange it happened on, in one place that adds them all together the same way the worked example above did.
That's what NetWort's Holdings page does. Log a buy transaction for every purchase you've made, whether it happened on Indodax, Pintu, Binance or anywhere else, all under the same asset in one portfolio. NetWort totals the cost and the quantity across every transaction you've entered and calculates your real, weighted average cost basis automatically, the same way the formula above did by hand. It doesn't matter where the trade actually happened. It only matters that you recorded it.
If you've never consolidated your purchases before, it's a one-time job, not an ongoing chore. Most exchanges let you export a transaction or trade history from account settings. Pull one from each exchange you've ever used, and for exchanges that don't offer an export, your order confirmations or account statements will usually carry the date, price and quantity of each trade.
Once you have the full list, enter each purchase as its own transaction against the same asset in your NetWort portfolio. Check the Asset Detail page for a coin's current price while you're at it, so you can see your real position update the moment your history is complete.