MTD Software: What Happens When Your Broadband Goes Down

April 2026 is closer than your next VAT return. And somewhere between now and then, your broadband will go down at the worst possible moment.

This is the MTD software question nobody in the industry wants to answer directly: what actually happens to your quarterly submission when the internet fails, your laptop dies, or HMRC's own systems go offline? The marketing brochures for every approved MTD software product are silent on this point. The HMRC guidance is vague. And the penalty regime for missed quarterly updates, which kicks in from April 2026 for sole traders earning above £50,000, is not.

The Quarterly Deadline Problem Nobody Talks About

Under Making Tax Digital for Income Tax Self Assessment (MTD for ITSA), sole traders earning above £50,000 must submit four quarterly updates plus a final declaration every tax year. That is five separate submissions annually, each with its own deadline. Miss one, and you accrue a penalty point under HMRC's new points-based penalty regime.

Four points means a £200 fine. A fifth missed submission adds another £200. The points do not reset until you have filed everything on time for two consecutive years. For a plumber or electrician earning £60,000 who simply forgot to check their software during a busy week on site, this is not a theoretical risk.

But here is the part that deserves more scrutiny: HMRC's 'reasonable excuse' framework, which can theoretically waive a penalty, explicitly excludes reliance on a third party. If your MTD software provider's servers go down on the last day of a quarterly deadline, that is arguably a third-party failure. HMRC's own guidance states that a reasonable excuse must be "something that stopped you meeting a tax obligation that you took reasonable care to meet." Losing internet access for a day may qualify. Your software vendor having a server outage almost certainly does not.

HMRC's Own Outage Record Is Not Reassuring

In January 2023, HMRC's online services experienced a significant outage affecting Self Assessment submissions during one of the busiest filing periods of the year. In 2022, the Government Gateway suffered intermittent failures across several weeks in October and November. HMRC acknowledged both incidents but offered no automatic penalty waivers; taxpayers had to appeal individually and demonstrate they had attempted to file.

This matters enormously for MTD software users because every approved product submits directly to HMRC's API. When HMRC's API is down, your software cannot submit, regardless of how reliable the software itself is. The submission pipeline has two potential points of failure: your software provider's servers, and HMRC's receiving infrastructure. You are responsible for the consequences of both.

To be fair, HMRC does operate a digital exclusion exemption process, and genuine technical failures can sometimes be appealed. But appeals take time, require evidence, and are not guaranteed. For a self-employed electrician with a van full of jobs and no accountant on speed dial, fighting a penalty appeal is a week of unpaid administrative work.

Cloud-Only vs Hybrid MTD Software: The Question to Ask Before You Buy

Most MTD software on the market today is cloud-based. Your records live on the provider's servers. You access them through a browser or app. When you submit a quarterly update, the software talks to HMRC's API in real time.

This architecture has genuine advantages: automatic backups, access from any device, no local installation. But it has one critical weakness that the sales pages rarely mention. If you cannot get online, either because your broadband is down, your mobile signal is weak, or the software provider's own servers are unavailable, you cannot submit.

Some software products offer offline data entry, syncing your records when a connection is restored. Others offer local desktop versions that store data on your own machine and only require internet access at the point of submission. A handful offer hybrid approaches. The key point is that this distinction is rarely highlighted in onboarding materials. You have to ask specifically: "Can I enter records offline? What happens if I cannot connect on the deadline day?"

If you are evaluating MTD software right now, this is the second question to ask, right after the price. The first question, incidentally, should be whether the software will remain approved and actively maintained beyond 2027, a point covered in detail in Making Tax Digital Free Software: The Expiry Date Problem.

What 'HMRC Approved' Actually Guarantees (And What It Does Not)

Being on HMRC's list of MTD-compatible software means a product can technically communicate with HMRC's API. It does not mean HMRC has audited the product's reliability, uptime guarantees, data security practices, or customer support quality. The approved list is a technical compatibility certification, nothing more.

As covered in HMRC MTD Software: How the Approved List Actually Works, the list includes products ranging from enterprise accounting suites costing hundreds of pounds per month to small apps that may be maintained by a single developer. The technical bar for approval is the same across all of them. The operational reliability is absolutely not.

For a sole trader earning £65,000 a year, the consequences of choosing an unreliable MTD software provider are asymmetric. The software vendor faces no penalty if their servers are down when you need to submit. You do. That asymmetry is worth sitting with before you sign a twelve-month software contract because it was the cheapest option on a comparison site.

The 'Reasonable Excuse' Minefield

HMRC's published guidance on reasonable excuses for late submission includes: serious illness, bereavement, delays caused by HMRC itself, and events outside your control. It explicitly excludes: relying on someone else to file on your behalf (unless they also had a reasonable excuse), and software or computer failure where you did not take reasonable steps to address the problem.

That last clause is doing a lot of work. "Reasonable steps" in a technical failure scenario likely means attempting an alternative method of submission. Under MTD, there is no paper alternative. There is no phone-in option. The only submission route is digital, through approved software. If your approved software is unavailable and you cannot find an alternative in time, you are in genuinely murky territory.

HMRC has said it will take a light-touch approach to penalties in the early months of MTD for ITSA, as it did with MTD for VAT. But "light touch" is not a legal protection, and it tends to evaporate once the initial rollout period ends. By 2027 or 2028, the penalty regime will be operating in full.

Practical Steps to Reduce Your Submission Risk

None of this is an argument against MTD software. It is an argument for being a more demanding customer when you choose it.

Submit Early, Not on the Deadline

The simplest risk mitigation available is also the least glamorous: do not wait until the last day of a quarterly period to submit. HMRC allows you to submit quarterly updates as soon as the quarter ends. If you submit a week early, a one-day outage becomes an inconvenience rather than a penalty.

Check Your Software Provider's Uptime History

Most software-as-a-service providers publish a status page showing historical uptime. Look for it before you subscribe. A provider with 99.9% uptime sounds excellent until you realise that is roughly nine hours of downtime per year, potentially clustered around high-demand periods like quarter-end deadlines when everyone is submitting simultaneously.

Keep a Local Backup of Your Records

Even if your MTD software is cloud-based, export your records to a spreadsheet or PDF at the end of each month. If your software provider goes bust, changes their pricing, or simply locks you out of your account, you still have your data. This is particularly relevant given the concerns raised in Making Tax Digital Accounting Software: The Switching Cost Nobody Quotes about data portability when you want to change providers.

Understand Your Mobile Fallback

If your home broadband fails, can you submit using your phone's mobile data? Test this before you need it. Some MTD apps work well on mobile; others are effectively desktop-only despite being marketed as mobile-friendly. The gap between "accessible on mobile" and "functional on mobile" is wide enough to drive a plumber's van through.

Read the Terms on Force Majeure

Your MTD software contract almost certainly contains a force majeure clause that limits the provider's liability for outages caused by events outside their control. Read it. It will tell you exactly what recourse you do not have if their servers fail on deadline day.

The Broader Accountability Gap

There is a structural problem at the heart of MTD that no individual software choice can fully solve. HMRC has mandated digital-only submission through third-party commercial software, without building a robust free public tool or providing any analogue backup route. The entire system depends on private infrastructure operating reliably, with the penalty burden falling entirely on the taxpayer when it does not.

This is a policy choice, not an accident. As explored in Best MTD Software: Why Complexity Is the Business Model, the commercial software market that MTD has created has significant lobbying power in its own right. The absence of a free, HMRC-built submission tool is a feature of that political economy, not an oversight.

For sole traders, the practical response to an imperfect system is to be more prepared than the system expects you to be. That means choosing MTD software with genuine offline capability or fast customer support, submitting well before deadlines, and keeping your own records rather than trusting entirely to the cloud.

TapTax is built specifically for sole traders who want the simplest possible MTD-compliant submission experience, without the bloat of enterprise accounting features you will never use. If you are weighing up your options before April 2026, it is worth understanding exactly what you are signing up for, including what happens when the internet decides to take a day off.