Got a quarter update wrong? MTD lets you fix an error before your final declaration

Now that Making Tax Digital (‘MTD’) for Income Tax is live, the question we hear from landlords more than any other is some version of this: “What happens if I get a quarter wrong?” People picture one slip of the keyboard locking them into a mistake, or a penalty landing because a figure was out by a few pounds.

The reassuring truth is that the system is far more forgiving than it first appears. Once you understand how the quarterly updates fit together, most of that worry falls away.

Your figures build up throughout the year

The first thing to understand is that your quarterly updates are cumulative. Each one covers the whole tax year-to-date.

So, your first update reports the period from the start of the tax year to the end of your first quarter. Your second update reports everything from the start of the year up to the end of your second quarter, with the first quarter rolled in. By the time you reach your fourth update, you have reported the full year’s running totals.

In other words, you are not filing four separate, sealed returns. You are updating one picture that grows as the year goes on.

How this feels in practice depends on your software. Some packages ask you to enter the cumulative year-to-date totals yourself. Others take just the latest quarter’s figures and add them to what you have already submitted, so the running total is worked out for you.

Why a wrong quarter is rarely a crisis

This is where the relief comes in. Because every update restates the year-to-date, a mistake in an earlier quarter does not sit there frozen forever. The next update simply overwrites the running total with the corrected figure.

Miscounted some rent in your first quarter? Forgot an expense? As long as your next set of year-to-date figures is right, the earlier error is absorbed into the corrected total. There is no separate, formal amendment to wrestle with, and no penalty for making the correction itself for an honest mistake.

Two simple ways to put something right

In practice, there are two ways to fix a figure:

1. Correct it in your next update. This is the most common route. If you spot the error after a deadline has already passed, you do not need to panic. Just make sure your next year-to-date figures are accurate by amending the quarter and letting the software send HMRC the updated when you next send in a quarterly update.
2. Resubmit the current quarter. If you catch the mistake before you have moved on to the next period, you can simply send that update again with the right numbers.

Either way, the process is built to let you keep things accurate as you go, rather than punishing you for an honest slip.

The final declaration/tax return is where everything is finalised anyway and your tax obligation is crystallised

It helps to think of your quarterly updates as a running estimate rather than the finished article. The point where everything becomes final is the final declaration, due by 31 January after the tax year ends.

That is where you confirm your figures, claim your reliefs and allowances, declare any other income, and make any year-end adjustments to reach your actual tax position. It is also your safety net. If you have sent all four quarterly updates and only then notice a mistake, you can still put it right at this stage, before anything is locked in.

The final declaration replaces the old Self-Assessment tax return. Because this is where your numbers are finalised, the quarterly updates along the way do not need to be perfect.

One thing worth being clear about

None of this is a licence to be careless. HMRC still expects reasonable care, and each update should be your best honest figure for the year so far. The point is not that accuracy stops mattering. It is that a single mistake in one quarter is simply not the disaster many landlords fear. You have right up until your final declaration to get the full picture right.

The short version

• Quarterly updates are cumulative, so each one covers the whole year to date.
• A mistake in an earlier quarter is fixed simply by getting the running total right in a later update.
• Nothing is set in stone until your final declaration on 31 January.
• Do your best each quarter, but do not lose sleep over a single wrong figure.

If MTD has been keeping you up at night, this is one part you can take off the worry list.

About the author: David runs SimplifyMTD, HMRC-recognised software for Making Tax Digital for Income Tax. Designed solely for landlords and free for landlords with UK and or foreign property income. You can find out more and can sign up at www.simplifymtd.com.