Koinly help UK
Koinly Numbers Wrong? How a UK Accountant Fixes Them
Your Koinly Report Says You Owe Tax You Don't Understand. Let's Find Out Why.
Koinly usually shows wrong numbers because of bad input data. Missing purchase history, unmatched wallet transfers, duplicate imports, and mislabelled DeFi transactions all push your figures off. A UK crypto accountant fixes this by rebuilding your data, applying HMRC's matching rules, and clearing every warning before anything reaches your tax return.
If you have searched for a Koinly wrong numbers fix at midnight before the filing deadline, you are not alone. Reddit threads are full of people staring at a £40,000 gain they know they never made. We sort out these reports for UK crypto holders every week, and we can sort out yours.
The cause
Why Are My Koinly Numbers Wrong?
Koinly calculates your tax from the data you feed it. When that data has gaps, Koinly fills them with assumptions, and those assumptions almost always make your tax bill bigger.
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The most common cause is missing history. If Koinly sees you selling Bitcoin but can't find where you bought it, it assigns a cost of zero. Your entire sale then counts as profit. One missing exchange from 2021 can add five figures to your gain.
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The second cause is one-sided data. Koinly sees coins leave Coinbase but doesn't see them arrive in your Ledger, so it treats the withdrawal as a sale. You didn't sell anything, but your report says you did.
What goes wrong
The Koinly Errors We Fix Most Often
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Missing Cost Basis Warnings
Koinly flags these as “missing purchase history” warnings on individual transactions. Each warning means Koinly has priced a disposal against zero cost. We trace every one back to its source, whether that's an old exchange, a peer-to-peer purchase, or a wallet you forgot about. Our missing data service covers exactly this problem.
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Transfers Between Your Own Wallets Show as Sales
Moving crypto between accounts you own is not a disposal for UK tax. But if Koinly can't match both sides of the transfer, it records a withdrawal and a separate deposit. The withdrawal looks like a sale. We match these transfers by amount, timestamp, and on-chain transaction hash. This fix alone often cuts a client's gain in half.
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Duplicate Imports From API and CSV
Connect an exchange by API and then upload a CSV file for the same account “just to be safe”. Koinly counts every trade twice. Your balances go negative, your disposals double, and your gain inflates. We remove the duplicates and check your closing balances against the real exchange balances.
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DeFi, Staking and Airdrops Carry the Wrong Label
Koinly can't always tell what a smart contract interaction means. A liquidity pool deposit might show as a sale. A staking reward might show as a gift. HMRC treats most staking, lending, and airdrop receipts as income at their sterling value on the day you receive them. That value then becomes your cost basis for the later sale. Wrong labels create two errors at once.
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The Wrong Tax Settings for the UK
Koinly lets you choose your country and cost basis method. If your account uses the wrong country, Koinly applies the wrong rules to every transaction. We check your settings first, because a single wrong toggle changes every figure on the report.
HMRC matching order
How Do UK Cost Basis Rules Work in Koinly?
A Koinly cost basis error UK users face usually comes from bad data meeting HMRC's strict rules. UK law doesn't let you choose FIFO or a simple average. HMRC matches every sale in this order: first against coins bought the same day, then against coins bought in the next 30 days, and finally against your Section 104 pool at its combined average cost.
Koinly's UK setting applies these rules automatically, but only when your dates, amounts and prices are correct. One trade on the wrong day, often from a CSV time zone error, can shift the cost basis for every later sale.
Your exchange's “average buy price” adds confusion because it only covers coins on that platform. HMRC pools the same asset across all your accounts, so the exchange figure is usually the wrong one to rely on.
What we do
What Does a Koinly Wrong Numbers Fix Involve?
We take your existing Koinly account and work through it methodically. You don't need to start again or switch software.
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1. We Review Your Account and Settings
We confirm your country, tax year, and cost basis method. We list every connected wallet and exchange, and we compare that list against what you actually used. Missing accounts become obvious at this stage.
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2. We Rebuild the Missing Data
We pull full histories from API exports, CSV files, and on-chain records. That includes exchanges that have closed, accounts you're locked out of, and wallets you haven't touched in years. Our crypto reconciliation service explains this process in more detail.
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3. We Clear Every Warning and Correct Every Label
We match transfers, remove duplicates, relabel DeFi activity, and resolve each missing cost basis warning. We then check your Koinly balances against your real closing balances on each platform. When they match, we know the data is complete.
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4. We Check the Final Figures and Prepare Your Return
We review the corrected capital gains and income figures against HMRC's rules. We apply your annual exempt amount, claim any losses you missed, and prepare the figures for your Self Assessment. If you want us to, we file the return as your agent and handle any HMRC questions that follow.
Most engagements take two to four weeks, on a fixed fee we agree before we start. The corrected figure is often much lower than the one that worried you, and sometimes it turns into a refund.
Your options
Should You Fix It Yourself or Hire an Accountant?
You can fix simple problems yourself. If you used one or two exchanges, never touched DeFi, and only have a few warnings, Koinly's own guides will get you most of the way.
An accountant makes sense for large gains, many platforms, DeFi or NFT activity, a closed exchange, or an HMRC letter. It also helps when you don't trust the number on your screen.
Many people searching for ‘Koinly Review Help UK’ consider Koinly's Expert Review, which checks your data inside the software. As a Koinly Expert Review alternative, a UK chartered accountant also takes responsibility for your figures, files your return, and deals with HMRC for you.
Still choosing a tool? Our crypto tax software comparison for the UK compares each option.
Already filed
What If You Already Filed With the Wrong Numbers?
You can correct it. You can amend a Self Assessment return online for up to 12 months after the 31 January filing deadline for that tax year. For older years, HMRC offers a voluntary disclosure route.
Acting early matters. HMRC now receives crypto exchange data automatically, and it treats a correction you make on your own far more favourably than one it has to prompt. If Koinly overstated your gain, you might be owed money back. If it understated your gain, fixing it now keeps penalties to a minimum.
Next step
Get a Koinly Report You Can Actually Trust
If your Koinly numbers don't make sense, don't file them and hope. We fix the data, confirm the figures, and give you a tax position you can defend to HMRC.
Questions
Frequently Asked Questions
Is Koinly Expert Review worth £799 or should I use an accountant?
Koinly's Expert Review checks your data inside the software. An accountant also takes responsibility for your figures, files your return, and deals with HMRC for you, which matters more if you have large gains, DeFi activity, or an HMRC letter.
How do I fix wrong numbers in Koinly?
Fix the data, not the final figure. Add every missing wallet and exchange, remove duplicates, match your own transfers, and clear every warning until your Koinly balances match your real ones.
Can Koinly file my UK tax return for me?
No. Koinly gives you reports to complete your Self Assessment, but you or your accountant must file the return with HMRC.
What do I do if Koinly and my exchange disagree on my cost basis?
Trust the corrected Koinly figure. Your exchange only sees its own coins, while HMRC pools the same asset across all your accounts using its own matching rules.