1. Using Estimated Figures Instead of Real-Time Data
One of the biggest mistakes we still see in 2026 is “guesstimating.” Some business owners look at their bank balance or a rough spreadsheet and plug in figures just to meet a deadline. In the eyes of HMRC, an estimate is an invitation for a compliance check.
HMRC expects your VAT returns to be a direct reflection of your digital records. With the 2026 requirements, your digital audit trail must be unbreakable. If you estimate a figure and it doesn’t match your underlying transactions, you aren’t just making a mistake, you are failing MTD compliance.
How to fix it: Stop the guesswork. Ensure your accounting software is synced daily with your bank feeds and sales platforms. If you are struggling to keep up, our team at Sterlinx Global handles the daily bookkeeping and calculations for you, ensuring that the figures we file are backed by actual data, not “finger-in-the-air” estimates.
2. Calculating VAT Using the Wrong Formula
It sounds simple, but calculating the actual VAT amount from a gross price is where many businesses trip up. If you are selling a product for £120 (including VAT), the VAT element is not £24 (20% of £120). It is £20.
Applying 20% to a gross figure instead of extracting the 1/6th properly results in overpaying or underpaying VAT. In a high-volume eCommerce environment, these small calculation errors can snowball into thousands of pounds of discrepancies over a financial year.
How to fix it: Memorize the formulas or, better yet, automate them.
- To add VAT: Net Amount × 1.20
- To extract VAT: Gross Amount ÷ 1.20 (or Gross ÷ 6)
- VAT Payable: Total Output VAT (Sales) – Total Input VAT (Purchases)
Using a structured compliance suite ensures these calculations are handled programmatically, removing human error from the equation.
3. Mixing Up Zero-Rated and Exempt Supplies
This is a classic trap, especially for businesses in the food, health, or publishing sectors. There is a massive legal difference between a “Zero-Rated” supply (0% VAT) and an “Exempt” supply.
- Zero-Rated: You charge 0% VAT, but you can still reclaim the VAT on the costs associated with making those sales.
- Exempt: You do not charge VAT, and you cannot reclaim VAT on any related expenses.
If you misclassify an exempt sale as zero-rated, you might be illegally reclaiming VAT, which will lead to a “Notice of Assessment” and potential penalties. This distinction is vital for food small businesses, where many products sit on the fine line between standard and zero-rated.
How to fix it: Review your product catalog against HMRC’s latest 2026 guidelines. Categorize every SKU correctly in your system so the tax treatment is applied automatically at the point of sale.
4. Applying the Wrong VAT Rates to Shipping and Fees
For eCommerce sellers, shipping is a major point of confusion. Many assume that because a product is zero-rated (like children’s clothes), the shipping should be too. However, the VAT treatment of delivery charges usually follows the “delivered goods.” If the goods are standard rated, the delivery is standard rated.
Furthermore, if you are selling globally, you must ensure you aren’t accidentally charging UK VAT to overseas customers where a different regime (or no VAT) applies. Mixing these up can lead to your prices being uncompetitive or your compliance being non-existent.
How to fix it: Audit your checkout settings. Ensure your tax engine distinguishes between domestic and international sales and applies the correct rate to ancillary charges like shipping and gift wrapping.
5. Errors in Key VAT Return Boxes (1, 4, and 5)
When filing via MTD software, the data usually flows into the boxes automatically, but that doesn’t mean it’s correct. Box 1 (VAT due on sales) and Box 4 (VAT reclaimed on purchases) are the two most scrutinized areas.
A common error is Box 4, where businesses try to reclaim VAT on items that are strictly prohibited, such as:
- Business entertainment (except for staff).
- Most motor cars.
- Purchases that are for personal use.
How to fix it: Before we submit a filing for our clients, we perform a reconciliation. You should do the same. Check Box 5 (the net VAT to pay or be refunded) against your expected margins. If the number looks “weird,” it probably is. If you’re unsure about what you can claim, talk to an expert to understand the process after a legitimate claim is made.
6. Misclassifying Error Size When Correcting Past Returns
Everyone makes mistakes, but how you fix them matters. In 2026, HMRC has strict thresholds for when you can simply adjust your next return versus when you must file a formal disclosure.
- Small Errors: If the error is under £10,000, or between £10,000 and £50,000 (but less than 1% of your Box 6 figure), you can usually adjust it on your next VAT return.
- Large Errors: If the error exceeds £50,000 or 1% of your outputs, you must report it specifically to HMRC using Form VAT652.
Attempting to “hide” a large error by trickling it through subsequent returns is considered a “deliberate” inaccuracy, which carries much higher penalties.
How to fix it: If you find a mistake, quantify it immediately. If it’s over the threshold, be proactive. Voluntary disclosure usually results in significantly reduced penalties. For more on the consequences of getting this wrong, talk to an expert.
7. Falling Behind on MTD for Income Tax (from 6 April 2026 if you’re over £50,000)
By 2026, the overlap between VAT compliance and the new MTD for Income Tax (ITSA) is real—and from 6 April 2026 it becomes mandatory for sole traders and landlords with qualifying income over £50,000. The mistake here is keeping your VAT records separate from your income tax records (or leaving the MTD setup until the last minute).
HMRC is moving toward a single digital view of a taxpayer. If your VAT returns show a certain level of turnover, but your quarterly ITSA updates show something else, it can trigger a red flag in HMRC’s system. Also worth noting: HMRC updated its manuals on 6 March 2026 around Permanent Establishment (PE).
