Salaried Americans at home rarely think about estimated tax, because payroll handles it. Move abroad, go freelance, or take income nobody withholds from, and the job becomes yours.
This guide covers who has to pay, how much, when, and how to handle the mismatch between American due dates and British tax you have not paid yet.
What is estimated tax?
It is tax you pay during the year on income nobody withholds from, rather than at the end. Self-employment profits, rental income, investment income and a foreign salary all commonly qualify.
The IRS states that individuals generally must pay if they expect to owe $1,000 or more on the return. The IRS page on estimated taxes sets out the rule.
Living outside the United States changes none of that. The obligation follows the income, not the address.
Who has to pay it from abroad?
Anyone whose expected balance crosses that threshold after counting withholding and any credits. For Americans abroad, that usually means the self-employed, landlords, investors, and anyone paid by a foreign employer.
An employee of a US company abroad may still have withholding, which can cover the year. Someone paid gross by a British employer has nothing withheld for the IRS at all.
In our practice we see the first year abroad cause the most trouble. Withholding stops, the income continues, and nobody sends a reminder.
How much do you have to pay?
Enough to reach a safe harbor. The IRS describes paying at least 90% of the current year's tax, or 100% of the tax shown on the prior year's return, whichever is smaller.
A higher percentage of the prior year applies to higher incomes, so check which figure fits you. Special rules also apply to farmers and fishermen.
The prior-year route is the practical choice for most people abroad. It uses a number you already know, rather than a forecast of a year still in progress.
Check the prior-year figure against the return you actually filed, not the one you meant to file. An amended return changes the number the safe harbor rests on.
| Question | Answer |
|---|---|
| Who pays | Anyone expecting to owe $1,000 or more |
| How much | 90% of this year, or 100% of last year, whichever is smaller |
| Higher incomes | A higher percentage of last year applies |
| How many payments | Four, one for each payment period |
| Form | Form 1040-ES |
When are the payments due?
The year splits into four payment periods, each with its own due date. Three of those dates fall inside the tax year itself, and the last one falls in January of the following year.
Due dates landing on a weekend or holiday shift to the next business day. The IRS page for Form 1040-ES carries the current dates and the worksheet.
Diary them at the start of the year. Missing one is the most common cause of an avoidable penalty.
Does the expat filing extension help?
Not with payment, and that trips people up every year. Americans abroad get an automatic extension to file, but the tax itself is still due at the ordinary deadline in April.
Interest runs from that ordinary date on anything unpaid. So a comfortable filing date does not mean a comfortable payment date.
Our guide to the October 15 deadline covers the filing extensions. Treat payment and filing as separate questions.
Why do foreign tax credits make this awkward?
Because the British tax that will remove your US bill often arrives later than the American due dates. Self Assessment settles in January, months after three of the four payment periods have closed.
You are still allowed to take expected credits into account when estimating. The risk is estimating wrongly and finding a shortfall at the end.
Our guide to avoiding double taxation explains how the credits work. The timing gap is a cash-flow problem more than a tax problem.
Paying British tax earlier than required does not fix the mismatch either. The credit follows the year the income belongs to, not the day the money moved.
Does the exclusion reduce what you pay?
It can reduce the income tax, but it does not touch self-employment tax at all. So a freelancer using the exclusion may still owe a substantial amount of estimated tax through the year.
That catches people who assume the exclusion removes everything. Our guide to choosing between the exclusion and the credit compares the two reliefs.
Where a certificate of coverage places you in the British social security system, self-employment tax falls away. Then the estimate drops sharply.
Does self-employment tax go into the estimate?
Yes, and for many freelancers abroad it is the largest part. The IRS page on self-employment tax for businesses abroad confirms the rules apply whether you live in the United States or not.
It also confirms that the foreign earned income exclusion does not reduce it. So the estimate has to cover the charge even in a year with no income tax at all.
A certificate of coverage changes that picture completely. Where British National Insurance applies to the same work, the American charge falls away and the estimate shrinks.
How do you actually pay from abroad?
Electronically, in almost every case, and the free options are the easiest. The IRS offers direct payment from a US bank account and an electronic payment system, both of which work from overseas.
Without a US bank account, an international wire is possible but slower and costlier. Some people keep a US account open purely for this reason.
Whatever the method, pay in good time. A payment that leaves your account on the due date may not arrive on it.
What if your income is uneven?
Then paying a quarter each period can overpay early and underpay late, which helps nobody. Freelancers with lumpy invoicing and investors with one large gain in December both run into this.
An annualized method exists for exactly that pattern. The IRS page for Form 2210 covers the calculation and the penalty rules.
It takes more work than four equal payments. For a genuinely uneven year, it can remove a penalty entirely.
What happens if you underpay?
The IRS charges a penalty that works much like interest on the shortfall, period by period. It is not a flat fine, so a small gap costs a small amount.
Paying late in the year does not undo an earlier shortfall. Each period stands on its own, which is why the safe harbor matters more than the final figure.
Withholding works differently from payments. Amounts withheld during the year generally count as paid evenly, which is occasionally useful.
Keep a note of what you paid and when. The calculation depends on dates, so a clear record shortens the work if a penalty is ever charged.
Can withholding replace estimated tax?
Sometimes, and that route is often simpler to run. Where you have a US employer, a pension or another payment subject to withholding, increasing it can cover the whole year.
That approach suits people with one steady American income stream and some untaxed income alongside it. It avoids four separate payment dates.
It does not suit a freelancer with no US withholding at all. Then estimated tax is the only mechanism available.
Do states expect payments too?
Some do, if you are still within a state's reach after moving. States with an income tax generally run their own estimated payment systems, with their own forms and their own due dates.
Someone who left a state cleanly usually has nothing further to pay. Someone who kept a home, a driver's license and a voter registration may not have left at all.
Our guide to filing a US return from the UK covers state residence in more detail.
Check the state rules in your first year abroad. A state that still counts you as resident will expect its own payments on the same income.
What if you overpay during the year?
The excess comes back through the return, either as a refund or as a credit against next year. Neither option is lost, although a refund takes time to arrive from abroad.
Applying an overpayment forward suits anyone who expects a similar year ahead. It also covers the first payment period without moving money internationally again.
Overpaying deliberately is still a cost. Money sitting with the IRS earns you nothing, so aim for the safe harbor rather than well beyond it.
Setting up estimated tax payments, step by step
Do this once at the start of the year, then repeat the payment four times.
Revisit the figures mid-year if your income changes sharply.
- Work out last year's total tax from the filed return.
- Decide whether the prior-year safe harbor or a current-year estimate suits you.
- Subtract any withholding you expect during the year.
- Divide the remainder across the four payment periods.
- Set up an electronic payment method that works from abroad.
- Diary all four due dates, including the one in January.
- Check in mid-year and adjust if income or credits have moved.
An illustrative example
Take an illustrative example: an American consultant in London leaves employment and starts invoicing clients directly. Her first year abroad produces a healthy profit and no US withholding at all.
She uses the prior-year safe harbor, since her old salary year gives a known figure. That protects her from penalties even though her new income is higher.
Her British tax settles the following January, and the credits remove most of the American liability. The payments she made come back through the return rather than being lost.
Common mistakes with estimated tax abroad
The first is assuming the June filing extension covers payment. It does not, and interest runs from the earlier date.
The second is relying on the exclusion to remove everything. Self-employment tax survives it, and it frequently dwarfs the income tax for a freelancer.
The third is skipping payments because credits will eventually cover the bill. The IRS tests each period separately, so a late credit does not fix an early gap.
The fourth is forgetting the January payment. It falls after the tax year ends, so it drops out of mind easily.
How US UK Tax Hub helps
We calculate estimated tax alongside both returns through our US federal returns service, including the credit timing that makes the first year abroad difficult. We set the four figures once and review them mid-year.
If nobody withholds tax from your income, send us last year's return and this year's expectations and we will set the schedule at a fixed fee agreed first. This article is general information, not personal tax advice; take advice on your own facts from a qualified adviser.