The letter from HMRC is never the first sign that something is wrong. It is the last.
For many higher-earning professionals living and working across Richmond, Twickenham, Kingston, and the wider South West London area, tax is something that happens largely in the background. Your employer deducts PAYE. Your pension contributions go through payroll. You file a Self Assessment return each January, or your accountant does, and a number comes back that you either expected or did not. The ones who sleep well are the ones who had a rough idea of the figure before it arrived. The ones who do not are the ones who assumed PAYE had taken care of everything, only to find that a combination of dividends, rental income, savings interest, and lost allowances has produced a bill they were not ready for.
This guide is about closing that gap. It walks through how to estimate what you owe, where the common surprises come from, and how to avoid the particular discomfort of discovering your tax position after the deadline rather than before it.
What you will learn
- Why PAYE alone does not always cover your full tax liability
- How to estimate your total income and tax position across multiple sources
- Where the most common surprises come from, with a worked example
- What to gather before you speak to your accountant
- How to avoid the January scramble
The income sources that catch people out
Dividends above £500 are taxable at 35.75% for higher-rate taxpayers and 39.35% for additional-rate. PAYE does not collect this.
Rental income is taxed at your marginal rate after allowable expenses. Mortgage interest relief is now a 20% tax credit only, which often surprises higher-rate taxpayers.
Savings interest above your Personal Savings Allowance (£500 for higher-rate, £0 for additional-rate) is taxable and must be declared.
The personal allowance taper: once your adjusted net income exceeds £100,000, you lose £1 of personal allowance for every £2 over that threshold. By £125,140, it is gone entirely, creating an effective marginal rate of 60%.
Why PAYE does not always cover what you owe
PAYE is designed to collect income tax and National Insurance on your employment earnings, and your employer’s payroll does this well. But it only knows about the income your employer is paying you. It does not know about your dividends, your rental property in Putney, the interest on your savings accounts, or the fact that your total income has crossed £100,000 and your personal allowance is being tapered away.
Each of those creates a tax liability that PAYE cannot collect.
This is why Self Assessment exists, not as a punishment but as a reconciliation mechanism. It brings together all your income sources, applies the correct rates and allowances, deducts what has already been collected through PAYE, and calculates the balance. For someone earning £95,000 through employment with no other income, the balance is usually nil or very small. For someone earning £95,000 with an additional £12,000 in dividends, £7,200 in rental income, and £1,800 in savings interest, the balance can easily reach several thousand pounds. Our earlier guide on Self Assessment obligations covers who needs to file and why, and the principles set out there feed directly into what follows here.
A worked example: estimating your liability
To make this concrete, here is a composite example based on the kind of professional we work with regularly across Richmond and South West London. The numbers are simplified but the patterns are real.
Total income of £134,000 puts this person comfortably into the higher-rate band, with the personal allowance fully tapered away because income exceeds £125,140. That taper alone adds roughly £5,000 to their tax bill compared to someone earning just under the threshold, because £12,570 of income that would otherwise be tax-free is now taxed at 40 per cent. This is one of the least understood features of the UK tax system, and it catches people in Richmond more often than you might expect, because salaries in the £90,000 to £110,000 range are common among professionals working in or commuting to central London. Add a modest dividend, a buy-to-let, or a savings pot built up over several years, and the threshold is breached without the person realising it. The effective marginal rate in the £100,000 to £125,140 band is 60 per cent, not 40 per cent. That figure surprises almost everyone who encounters it for the first time.
Here is how the rough calculation works.
The estimate of roughly £7,500 is a bill that will arrive through Self Assessment, on top of everything already deducted through PAYE. For someone who was not expecting it, that is an uncomfortable January. For someone who estimated it in advance and set the money aside, it is just administration.
The calculation above is deliberately simplified. Student loan repayments, pension relief claimed outside payroll, charitable giving under Gift Aid, capital gains, and other adjustments can all change the figure. The point is not precision. It is orientation, knowing roughly where you stand before the final number arrives.
The pieces most people forget
The income itself is usually not the problem. Most people know what they earn.
What they forget, or do not realise, is the interaction between those income sources and the allowances and reliefs that apply to them. The dividend allowance dropped to £500 from April 2024, which means almost all dividend income above that level is now taxable. The personal savings allowance reduces from £1,000 to £500 for higher-rate taxpayers, and disappears entirely at the additional rate. Mortgage interest on buy-to-let properties has not been fully deductible since 2020, which means a landlord paying £800 a month in mortgage interest only receives a 20 per cent tax credit rather than full relief at their marginal rate. Our personal tax guide for higher earners covers these allowance changes in more detail.
Pension contributions are the other area that regularly gets overlooked, not because people forget to make them, but because they forget to claim the additional relief. If you contribute to a personal pension and you are a higher-rate taxpayer, you are entitled to claim the difference between basic-rate relief, which is applied at source, and higher-rate relief, which must be claimed through your tax return. Missing this can cost several hundred pounds a year, and it is one of the simplest tax planning adjustments available.
Capital gains are a separate calculation but they affect your total tax position because they sit on top of your income for rate purposes. If you sold an investment, a second property, or shares during the year, the gain needs to be estimated and included in your thinking even if the formal reporting happens separately. Our guide to keeping property records covers the cost evidence that reduces a CGT bill, and the same principle applies to any chargeable asset.
What to gather before you speak to your accountant
The single most useful thing you can do is assemble your evidence pack before the conversation rather than during it. This is not about doing your accountant’s job. It is about making sure the conversation is about strategy and planning rather than chasing missing documents. Your accountant can do much more for you when they have the full picture in front of them, and Xeinadin’s accounts service is designed around exactly that kind of partnership.
Start with four things.
Your P60 from your employer, which confirms your salary and the tax deducted. Your dividend vouchers or a note of total dividends received, which your company accountant or registrar can provide. A summary of your rental income and expenses, even a rough one, covering rent received, mortgage interest paid, insurance, repairs, and agent fees, which is much easier to compile if you have maintained decent bookkeeping throughout the year. And your savings interest certificates, which your bank should provide or which you can find in your online banking. With those four documents, your accountant can build an accurate estimate of your position and identify whether there is anything that can still be done to reduce the liability, such as a pension contribution before the year end or a capital gains loss that can be offset.
Avoiding the January scramble
The professionals who find Self Assessment stressful are almost always the ones who leave it until December. The ones who find it manageable are the ones who treat it as a rolling process, gathering documents as they arrive during the year and having a short planning conversation with their accountant well before the deadline.
If you are employed and your tax affairs are relatively straightforward, a single conversation in September or October is usually enough to estimate the liability, identify any planning opportunities, and file the return in good time. If you have rental income, dividends, capital gains, or overseas interests, an earlier conversation, ideally in the summer, gives more room to act on the findings. The difference between a tax bill that arrives as a surprise and one that arrives as confirmation of something you already knew is usually one meeting.
That meeting is worth having.
If you are a higher-earning professional in Richmond or the surrounding area and you are not sure where you stand with HMRC, a short conversation can usually clarify the position and put a plan in place. There is no obligation and no agenda beyond making sure you know what is coming before it arrives. You can reach our Richmond team here.
About the author
Donovan Crutchfield is Area Managing Partner at Xeinadin Richmond and founder of TaxAgility. He is ACA-qualified and works with owner-managed businesses, professionals, and growing SMEs across Richmond-upon-Thames and South West London.
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