Roth IRA vs ISA: Is a Roth IRA the Same as an ISA? 2026 Limits Compared

Michael Whitman · Trading since 2017, full-time since 2020 · YouTube creator, 137K subscribers · Published 2026-09-08 · Updated 2026-11-02 · Reviewed 2026-11-01

Close, but not the same: both shelter growth on money you have already paid tax on, and that is where the likeness ends. A Roth IRA is an American retirement account that holds $7,500 a year in 2026, and a stocks and shares ISA is a British account that holds £20,000 a year and lets you take every penny out whenever you want.

The tax idea is shared. The size, the access rules and who is allowed to open one are not, and those three differences are what decide how useful each account is in practice.

What each one is

A Roth IRA is an individual retirement account in the United States. You pay in from income that has already been taxed, the investments grow without yearly tax, and withdrawals of growth are tax-free once the account passes the IRS test for a qualified distribution. The Roth IRA page covers how it works on its own.

A stocks and shares ISA is the United Kingdom’s individual savings account for investments. Money goes in after tax, nothing inside is taxed, and GOV.UK says you can take money out at any time without losing the tax benefits. The stocks and shares ISA page covers it in full.

Where they differ

The headline rules side by side, each read on the official page on 1 November 2026:

Access is the difference that matters most. In a Roth IRA, the IRS ordering rules treat your regular contributions as the first money out, so what you paid in is reachable before retirement.

The growth is the part held back: take it before the five-year period and age 59½ and it is taxed as income, with a 10% additional tax on top unless an exception applies. An ISA has no such line. Contributions and growth are the same pot, and the whole pot can come out.

The yearly room is lopsided. £20,000 converted at the 6 April 2026 rate was $26,470, so the ISA takes 3.53 times what a Roth IRA under 50 can take this year, and the IRA figure covers traditional and Roth accounts together rather than each one.

Eligibility follows residence, not passport. GOV.UK limits new ISA payments to UK residents. If you move abroad you can keep the ISA and its tax relief, but you cannot pay into it until you are resident again. The Roth IRA needs taxable compensation instead, and the IRS says compensation does not include foreign earned income you exclude from tax, which is the trap for Americans working overseas.

A worked example: ten years maxed into the same fund

The cleanest way to see the gap is to fill both accounts to the limit every year and buy the same thing in each. Here is that test with real prices, set up so the only differences are the two sets of rules.

The setup. From 2017 to 2026, the Roth IRA saver pays in the IRS limit for savers under 50 on the first US trading day of each January: $5,500 in 2017 and 2018, $6,000 from 2019 to 2022, $6,500 in 2023, $7,000 in 2024 and 2025, and $7,500 in 2026.

The ISA saver pays in £20,000 on the first US trading day on or after 6 April each year, converted to dollars at FRED’s rate that day.

Both buy SPY, an S&P 500 fund, with dividends reinvested through Yahoo Finance’s dividend-adjusted closes, and both are valued on 23 October 2026, the latest day FRED had a pound rate. The ISA’s shares are bought in dollars and its balance is converted back to pounds at FRED’s 23 October rate. A UK saver would usually hold a UK-listed S&P 500 fund rather than SPY itself; SPY is used here so both accounts hold the identical fund.

The Roth IRA. $63,000 paid in had become $141,650. That is $78,650 of growth, or 124.84%. Under the ordering rules the $63,000 of contributions, 44.48% of the balance, could come out before retirement; the $78,650 of growth waits for the five-year and age 59½ test.

The ISA. £200,000 paid in had become £448,772, which is $600,232 at the 23 October rate of $1.3375. Growth in pounds was £248,772, or 124.39%. Every pound of it could be withdrawn the next day.

What the example shows. This is not one account beating the other. The two follow different yearly limits in different currencies, so the balances measure the size of each allowance, not the quality of the account.

Measured in each account’s own currency the growth rates were close, 124.84% in dollars for the Roth and 124.39% in pounds for the ISA, partly by coincidence, since the fund was the same but the currencies were not. Counted in dollars the ISA grew 130.99%, from $259,852 to $600,232; the gap comes from its April purchase dates and the pound’s moves, not from the wrapper. The ISA ended 4.24 times bigger in dollars because it took about four times as much money in, and its whole balance stayed reachable. The Roth IRA’s advantage is a US one: its growth is tax-free under US rules, which matters to anyone who will be a US taxpayer when the money comes out.

Which one to use: Roth IRA or Stocks and Shares ISA?

Use the ISA when you are UK resident, and use it first when the money might be needed before retirement, because nothing inside it is locked. If you also want a pension-style account, the nearest UK match to a traditional IRA is the SIPP.

Use the Roth IRA when you are a US taxpayer with earned income under the phase-out, and treat it as retirement money even though contributions can come back out. If your income is above the phase-out, the backdoor Roth is the route people use.

When both systems touch you, get cross-border advice before paying into either. The IRS taxes US citizens on worldwide income wherever they live, and the ISA’s shelter is a UK rule, so a US citizen in Britain cannot assume the ISA works for them the way it works for a neighbor.

What changes in April 2027

The overall £20,000 stays, but cash gets a sub-limit. HMRC published the measure on 17 September 2026: from 6 April 2027, savers under 65 can put no more than £12,000 a year into cash ISAs, with restrictions on moving money from stocks and shares ISAs into cash ISAs. Over-65s keep a £20,000 cash limit.

A stocks and shares ISA, the account on this page, can still take the whole £20,000. The Roth IRA’s limit, by contrast, is reset by the IRS through its yearly cost-of-living adjustments.

The original data

Both limits in one currency, every year since the ISA reached £20,000. HMRC’s statistics table shows the overall ISA limit at £20,000 from the 2017-18 tax year onward, and GOV.UK gives the same figure for 2026-27. The table converts it at FRED’s noon rate on 6 April, or the last US business day before it, and sets it against the IRS limit for the calendar year in which that tax year starts (IRS Publication 590-A for 2017 to 2022, the IRS limits page for 2023 to 2026).

The gap is narrowing, slowly. Over the ten years the ISA allowance totaled $260,128 at those rates and the IRA limit $63,000, 4.13 times as much.

The IRA limit rose 36.36% from 2017 to 2026 while the ISA stayed frozen in pounds, so the multiple fell from 4.54 to 3.53, with the pound’s swings moving it around in between. At FRED’s latest rate, $1.3375 on 23 October 2026, £20,000 was $26,750. Every conversion is in the allowance file.

The worked example, drawn. The second chart splits each account’s 23 October 2026 balance into what was paid in and what it grew to, with the purchase dates, rates and prices in the worked-example file.

How the figures were checked. Yahoo Finance’s daily pound closes sat within 1.43% of FRED’s rate on all 14 exchange-rate dates used, the widest gaps on 4 and 7 April 2025, days the pound moved sharply (Yahoo’s close and FRED’s noon New York rate are taken at different times of day), and SPY’s closing prices from Yahoo matched Nasdaq’s to the cent on all 21 purchase and valuation dates.

The ISA paid in $259,852 at the purchase-day rates in the chart, slightly less than the $260,128 in the table: 6 April fell on a weekend in 2019, 2024 and 2025, and the table uses the Friday rate before it while the purchases use the Monday after.

The example ignores fees and any tax withheld on dividends, so both balances are a little high.

Coverage is lopsided as well. In the 24,971-video search study behind this site, the Roth IRA appears in 24 titles across 15 channels at a median of 95,293 views, and ISAs in 4 across 3 at a median of 23,040, each video counted once.

When it fails

The common failure is using one country’s rules on the other country’s account. A reader in Leeds hears an American video say growth is locked until 59½ and leaves an ISA untouched for a house deposit it could have paid for; a reader in Ohio hears that a tax-free account can be emptied at any time and pulls Roth growth early, then meets income tax and the 10% additional tax.

The second is quoting an old limit. One comparison page that ranks for this search still lists the Roth limit at $7,000 and a phase-out below the IRS’s 2026 range. The IRA limit has changed four times since 2017; check the IRS page each January.

The third is assuming eligibility moves with you. An ISA cannot take new money while you live abroad, and a Roth IRA cannot take money backed only by excluded foreign income.

Questions people ask

Is a Roth IRA the same as an ISA?

No, though they share the tax idea: both take taxed money and shelter the growth. The ISA holds more (£20,000 against $7,500 in 2026), has no income test and no retirement condition; the Roth IRA keeps its growth back until the five-year and age 59½ test is met.

Can a US citizen have an ISA?

A US citizen who is resident in the UK and 18 or over meets GOV.UK’s rules for opening one. The IRS still taxes US citizens on worldwide income, and the ISA’s shelter is a UK rule, so take cross-border tax advice first.

What are the disadvantages of a Roth IRA?

A small yearly limit ($7,500 in 2026, shared with traditional IRAs), an income phase-out from $153,000 for single filers, and earnings that can be taxed plus a 10% additional tax if taken before the qualified-distribution test, unless an exception applies.

How much will $10,000 make in a Roth IRA?

It depends entirely on what it is invested in, and $10,000 is more than one year’s limit. As a past reference, $10,000 in SPY on 3 January 2017 with dividends reinvested was worth $39,277 on 23 October 2026. That is history, not a forecast; the Roth IRA growth calculator runs your own numbers.

What happens to an ISA if I move to the US?

You can keep it and its UK tax relief, but you cannot add to it until you are UK resident again. How the US taxes it is a separate question for an adviser.

Related

Roth IRA explains the US account step by step, and how to open a Roth IRA walks through the setup. On the UK side, stocks and shares ISA covers the account itself and cash ISA vs stocks and shares ISA covers the choice the 2027 change affects. For money with no shelter in either country, brokerage account is the comparison.

This page is educational, not financial advice. Test every idea on your own charts before risking money.