Estimated tax payments from the UK: the September 15 date most expats miss

Figures relate to tax year 2025 (US)

US estimated tax payments are quarterly prepayments the IRS expects when no employer withholds your American tax. Living in the UK changes nothing about that machinery. Once your US return will show $1,000 or more due, the IRS wants the money during the year. And the third installment for 2025 income lands on September 15.

Most expats never owe these payments, because foreign tax credits wipe their US bill. But the exceptions are common enough to check every year. So this guide covers who pays and how much. It also walks through the safe harbors that cap the math, plus the mechanics of paying from a UK bank.

Key takeaways

• Quarterly payments apply when your final US bill will reach $1,000 after credits and withholding.
• Safe harbors cap what you must prepay: 90% of this year's tax, or 100% of last year's (110% at higher incomes).
• The 2025 due dates: April 15, June 16 and September 15, 2025, then January 15, 2026.
• Most UK-based employees owe nothing, because UK tax paid generally exceeds the US charge.
• US-source income — rents, dividends, Roth conversions, business profit — is what usually creates a bill.

What is an estimated tax payment?

It is a direct quarterly prepayment of your own US income tax, made because nobody withholds it for you. American employees prepay invisibly through payroll withholding. Expats and the self-employed lack that machinery, so the IRS collects through four dated installments instead.

The legal trigger is simple. According to the IRS estimated taxes guidance (opens in a new tab), the duty starts when you expect to owe at least $1,000 with the return. Below that line, no quarterly duty exists. You simply settle everything the following April.

Do expats in the UK really owe quarterly payments?

Usually not, and the reason is the foreign tax credit. UK tax rates generally exceed American ones. So credits for tax paid to HMRC wipe the US bill on UK salary and most UK investment income. No expected bill means no estimated tax payments — the duty simply never switches on.

The exceptions cluster around income the UK taxes lightly or later. In our practice we see the same triggers each year:

• US rental profit, which UK tax may not fully shelter after depreciation differences
• US dividends, interest and capital gains held outside UK taxation timing
• Self-employment profit, where US self-employment tax can apply without a totalization certificate
• Roth conversions and IRA withdrawals taken while abroad
• A UK bonus year where the credit timing lags the US liability
• Owing over $1,000 last April — the strongest predictor of owing again

The safe harbor rules that cap what you pay

You never have to guess the year perfectly. Instead, the rules excuse any underpayment penalty when your four installments reach a safe harbor. Two harbors exist, and you may use whichever is smaller.

The prior-year harbor is the expat favorite, because last year's number is already known. Pay a quarter of it on each date, and penalties cannot touch you even when this year's income jumps. Then the balance simply settles with the return.

When are estimated tax payments due in 2025?

The IRS calendar runs on uneven quarters, which surprises everyone at least once. For 2025 income, the dates fall on April 15, June 16 and September 15 of 2025. The final installment then follows on January 15, 2026. Weekend shifts move a date forward a day in some years.

Note what the June expat extension does not do. The automatic two-month extension moves your filing date, yet estimated tax payments keep their own calendar. Per the IRS pages for citizens abroad (opens in a new tab), interest still runs from the original dates. Living overseas changes paperwork, never payment timing.

How to pay the IRS from the UK, step by step

Paying from Britain takes minutes online, and no US bank account is required for card routes. Here is the clean sequence we use with clients making estimated tax payments from the UK:

1. Work out the installment: normally one quarter of your chosen safe harbor amount.
2. Sign in to IRS Direct Pay (opens in a new tab) or your IRS online account — Direct Pay draws on a US bank account free of charge.
3. No US account? Use the card processors listed on the IRS payments page, or a dollar balance in a multi-currency account.
4. Select 'Estimated Tax' as the reason, Form 1040-ES, and tax year 2025.
5. Pay by the installment date, US time, and save the confirmation number.
6. Log the payment where your preparer will find it — every dollar prepaid must appear on the return to count.

The June extension moves your paperwork. It has never once moved your money.

Pounds in, dollars out

Every installment is due in dollars, so sterling earners carry exchange risk between quarters. A simple habit tames it. When a US bill is building, move the rough amount into dollars as the income arrives, rather than converting everything in a rush the night before a deadline.

Keep the conversion records too. The return itself translates income at published rates, while your payments clear in actual dollars. Those two numbers never quite match, and tidy records are what make the difference boring instead of stressful.

Two systems, two prepayment calendars

Dual filers juggle a British cousin of the same idea: HMRC's payments on account, due each 31 January and 31 July. The two systems never coordinate. Each looks only at its own liability, on its own dates, in its own currency.

That independence matters for cash flow. A self-employed dual filer can face HMRC in January, the IRS in January, HMRC again in July, and IRS quarters in between. Map the whole year once, in September, and none of those dates arrives as a surprise again.

Income that changes mid-year

When income arrives unevenly — a property sale in November, say — equal quarters can overcharge the early year. The annualized income method fixes that. It matches each installment to the income actually earned by that date, using a schedule filed with the return.

The method costs extra calculation, so most people reserve it for genuinely lumpy years. For steady incomes, the prior-year harbor stays simpler and just as safe. And whichever route you choose, keep it consistent through the year — switching methods mid-stream is where avoidable penalties usually creep in. A quick check each quarter, against income actually banked, keeps the whole system honest.

What happens if you skip a payment?

The cost is an interest-style penalty on the shortfall, computed quarter by quarter until paid. Rates float with the federal short-term rate, so recent years have priced procrastination at roughly 7-8% annually. The IRS underpayment penalty page (opens in a new tab) sets out the mechanics and the current figure.

Because it works like interest, a missed September payment costs little when corrected in October. Left until the following April, the same miss compounds across seven months. So the practical rule is simple: pay late rather than never, and pay the moment you notice.

A worked example

Take an illustrative example. A consultant in London earns £80,000 from UK clients, fully taxed by HMRC. She also keeps a US rental portfolio producing $30,000 of profit. Her 2024 return showed $4,800 of US tax after credits, so for 2025 she chooses the prior-year safe harbor.

That makes each installment $1,200, paid in April, June and September 2025, then January 2026. Her UK salary needs no US prepayment, because credits cover it entirely. When the rental profit rises in 2025, the extra settles penalty-free with the return. Her safe harbor held all year, so no penalty can attach.

The mistakes that create penalties

Estimated payment problems rarely come from arithmetic. Instead they come from assumptions, and the same few repeat across the files we repair each autumn:

• Assuming the June filing extension also delays the June and September money — it does not.
• Ignoring US-source income because 'the UK taxes me now', when the credit timing does not align.
• Skipping the safe-harbor check after a first year of owing, then repeating the penalty.
• Forgetting self-employment tax, which foreign tax credits never offset, absent a totalization certificate.
• Paying HMRC's payments on account and assuming the IRS shares the information — the systems never talk.
• Making the payment but leaving it off the return, so the IRS shows a mismatch either way.

The self-employment trap deserves special attention for freelancers. Our guide to self-employment as an American in the UK covers the certificate that matters there. It keeps 15.3% of profit out of the IRS's reach. For the broader annual picture, start with what Americans in the UK actually file.

How US UK Tax Accountants helps

We calculate safe harbors as part of every US federal return we prepare. So the four dates arrive with numbers attached rather than guesswork. One senior specialist watches both systems together, HMRC's payments on account beside the IRS quarters. Then credit timing gets planned so you never prepay the same income twice.

Fees are fixed and agreed in writing before any work begins. When a quarter genuinely owes nothing, we say so plainly, and the reminder that lands in your inbox simply confirms it. Either way, September never has to arrive as a surprise again.

Before September 15

If a 2025 US bill is building from rentals, dividends or a conversion, September is the cheap moment to act. Tell us your income picture. We will confirm whether estimated tax payments apply, size the installment against your safe harbor, and handle the mechanics. Book a consultation and hear back within one working day.

Last reviewed 7 September 2026 by the US UK Tax Accountants Tax Team. This article is general information, not personal tax advice — speak to a qualified US/UK tax adviser about your own position.

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