Our Cash ISA returns calculator is a simple tool that helps you visualise how your savings could grow over time.
By adjusting the inputs, you can quickly see how factors such as interest rates, regular contributions and time affect your returns. This can help you make more informed decisions about where to place your savings and how much you need to contribute to reach your financial goals.
Switch To A Better Paying Cash ISA
Cash ISAs are individual savings accounts that are structured as a “tax wrapper” which just means there’s no tax on the interest you earn from money in the account. We’ve scoured the market to find the best interest on cash ISAs so you can make more from your savings.
Description:Online trading platform XTB has launched a headline-grabbing 6% AER flexible Cash ISA, instantly placing it among the most competitive easy-access ISA rates on the market. At first glance, it looks like a market-leading deal. However, the generous rate comes with important conditions that savers should understand before transferring funds.
The advertised 6% AER is not a fixed long-term rate. It is made up of a 4% standard variable rate plus a 2% promotional boost. That boost lasts for 90 days from the date the ISA is opened. After the 90-day period ends, the rate automatically reverts to XTB’s standard variable rate, currently 4% AER.
Crucially, the offer only applies to new clients who open a Cash ISA or Stocks & Shares ISA between 1 March and 30 April 2026. If you open outside that window, you will not receive the 6% rate. Existing clients receive the standard 4% variable rate from the outset.
The Rate Is Variable?
Even after the promotional period ends, the 4% rate is not guaranteed. XTB’s ISA terms confirm that interest is calculated daily and credited monthly at a variable rate that may change. This means the base rate could rise or fall depending on market conditions. The 6% headline figure is therefore a short-term incentive rather than a fixed return.
Is Your Money Held in a Bank or a Money Market Fund?
Another key consideration is where client money is held. XTB states that Cash ISA funds may be placed in segregated client money bank accounts or in one or more Qualifying Money Market Funds (QMMFs).
If funds are placed in a QMMF, they are not treated as bank deposits and do not benefit from traditional FSCS deposit protection in the same way as money held in a bank account. Instead, they fall under FCA client asset rules, with FSCS investment protection potentially applying in the event of firm insolvency, but not against investment losses.
XTB’s 6% Cash ISA is competitive, but only for three months. After that, savers revert to a variable rate that could change. Combined with the possibility that funds may be held in a money market fund rather than a traditional bank account, the headline rate deserves closer inspection before making a decision.
If you are putting money away in the long run, the stock market can offer much better returns, so investing in a stocks and shares ISA may make you more money.
Description:Tembo’s Easy Access Cash ISA offers a competitive headline rate and a simple mobile-first savings experience. With 4.45% AER and unlimited withdrawals, it looks attractive for savers wanting flexibility and tax-free interest. But as with many high-rate ISAs, part of the return relies on a temporary bonus that investors should understand before opening.
Tembo’s Easy Access Cash ISA allows savers to earn 4.45% AER (variable) on up to the annual ISA allowance of £20,000 per tax year, while keeping interest tax-free under the ISA wrapper. The account is designed to be simple and app-based, allowing customers to track their balance and interest growth through the Tembo mobile app.
Interest accrues daily and is paid monthly, which helps savers benefit from compounding over time. The account also offers unlimited withdrawals without reducing the interest rate, making it suitable for people who want access to their savings without locking money away. Withdrawals can take up to two working days to process.
One unusual feature is that Tembo links its savings accounts with its mortgage brokerage service. Customers who open a Tembo savings account are offered fee-free mortgage advice, which the company promotes as an added benefit for those saving for a house deposit.
Savings held through Tembo are protected by the Financial Services Compensation Scheme (FSCS), although the protection level depends on the underlying partner bank where the funds are held. Tembo states that funds are protected up to £120,000, reflecting the structure of its savings arrangements.
Is There a Catch?
The headline 4.45% rate includes a temporary bonus. The underlying rate is 3.4% AER, with an additional 1.05% bonus for the first 12 months. Once the bonus expires, the rate will fall unless Tembo increases the underlying rate.
Another limitation is that ISA transfers are currently not accepted, meaning you cannot move an existing ISA into the account. This restricts the product mainly to new ISA contributions rather than people consolidating older ISA savings.
Overall, Tembo’s Cash ISA is competitive for new savers who want flexibility and a strong introductory rate, but the bonus structure and lack of transfers mean it’s worth reviewing the rate again after the first year.
Description:Moneyfarm’s Cash ISA offers a competitive introductory rate and flexible access to tax-free savings. With a boosted first-year return and daily interest, it aims to combine the simplicity of a savings account with the convenience of an investment platform. However, the headline rate comes with several conditions that savers should understand.
Moneyfarm’s Cash ISA allows savers to earn tax-free interest on cash savings, with a current introductory rate of 4.33% AER (variable) in the first year. After 12 months, the rate drops to 3.51% AER (variable).
Interest is calculated daily, and you can deposit up to the £20,000 annual ISA allowance each tax year. Moneyfarm also allows free ISA transfers, so existing Cash ISA balances can be moved into the account without affecting your annual allowance.
Unlike traditional bank savings accounts, Moneyfarm holds customer cash in Qualifying Money Market Funds (QMMFs). These funds invest in short-term, low-risk instruments and are designed to act like cash while generating interest. The rate paid on the account is linked to the yield of these funds, meaning it can change if market rates move.
The account also offers some flexibility, allowing withdrawals when needed without penalties.
What’s the Catch?
The 4.33% headline rate only lasts for the first 12 months, after which the account reverts to 3.51%.
To maintain the boosted rate, savers must keep at least £500 in the account and limit withdrawals to three per year. Exceeding this reduces the rate to the lower level.
Finally, because savings are held in money market funds rather than a bank deposit, returns are variable and can change depending on market conditions.
Description:Lightyear’s Cash ISA currently pays 3.75% AER, designed to closely follow the Bank of England base rate. The account is fully flexible, has no account fees, no withdrawal penalties and no minimum deposit, and avoids short-term bonus rates that later drop. Savings are held across UK banks and qualifying money market funds, with FSCS protection applying to cash held in partner banks.
How does the Lightyear Cash ISA compare with rivals?
The Lightyear Cash ISA remains competitive thanks to its simple pricing, flexible terms and rate that tracks the Bank of England base rate, currently 3.75% AER (variable). You can withdraw and replace money without affecting your £20,000 ISA allowance, and there are no account fees, transfer charges or short-term bonus rates that later drop.
While the rate is solid, it now sits more in the middle of the market in 2026, with some rivals like Tembo offering slightly higher easy-access ISA rates. However, many of those come with bonus periods, withdrawal limits or tiered rates that can fall after the first year. Lightyear’s appeal is its straightforward approach: one variable rate that follows the base rate and no penalties for withdrawals.
Lightyear UK is authorised and regulated by the Financial Conduct Authority (FCA). FSCS protection applies to cash held with partner banks (typically up to £85,000 per person per bank), though this protection does not apply to money held in qualifying money market funds.
Description:CMC Invest’s flexible Cash ISA pays 3.69% AER (variable) with tax-free interest calculated daily and paid monthly, offering unlimited withdrawals without reducing the rate and a £1 minimum deposit to get started.
Customers can easily transfer existing ISAs in-app, benefit from FCA regulation and protection of client money, and access the account within CMC’s wider investing platform, which serves over 1.5 million global users. The ISA is fee-free to hold (with an optional £15 urgent withdrawal fee) and sits alongside CMC Invest’s subscription plans that add investing features, lower FX fees and broader market access for those using the wider platform.
Description:Wealthify’s easy-access Cash ISA pays 3.35% AER (variable) with tax-free interest paid monthly, no fees and flexible withdrawals that don’t affect your ISA allowance. The account is powered by ClearBank, meaning deposits are FSCS-protected up to £120,000 per person per banking licence, and sits within Wealthify’s award-winning platform backed by Aviva.
Rates:Wealthify’s Cash ISA currently pays 3.35% AER (3.30% tax-free p.a., variable) with interest calculated daily and paid monthly. Because the rate is variable, the amount you earn can rise or fall over time, typically moving in line with changes in the wider interest-rate environment. One advantage of using Wealthify is that savers can easily move into investment products on the same platform if savings rates fall and they want the potential for higher long-term returns.
As Wealthify’s Cash ISA interest rate is variable, the amount of money you get monthly will go up and down in line with any rises or falls in the Bank of England’s base rate.
But, the good thing about saving with Wealthify is that if rates go down again, you can switch into investments. One of the things that came up when I interviewed the then Wealthify CEO Andy Russell, back in 2020 was that it’s hard to educate people to invest rather than save, so hopefully, this may be people’s first step into a wider world of investing.
Market access & protection:Wealthify’s ISA is also flexible, so you can withdraw and replace money within the same tax year without affecting your £20,000 ISA allowance.
However, as the FSCS’s compensation limit of £120,000 is per banking licence, and the Wealthify Cash ISA is powered by ClearBank, this means the £120,000 limit is shared across all accounts you hold with ClearBank. For example, if you have £100,000 saved in a Wealthify Cash ISA and £40,000 saved in another account powered by ClearBank elsewhere (including the Wealthify Instant Access Savings Account), only £120,000 of your deposits would be eligible for FSCS protection.’
App & platform:Wealthify’s website and app are simple and beginner-friendly, making it easy to open and manage a Cash ISA online.
Customer service: Although there are no branches, customers can contact Wealthify’s UK-based support team by phone, email or live chat if they need help.
Research & analysis:Wealthify provides guides, blogs and educational content about saving and investing, helping users learn more if they decide to move from cash savings into investments in the future.
Our Cash ISA returns calculator helps you estimate how much interest your savings could earn over time. By entering a few simple details such as your starting balance, interest rate and monthly contributions, the calculator will project how your savings could grow.
It’s designed to help you understand how interest compounds over time and how small changes to contributions or interest rates can significantly affect your final balance.
Because Cash ISAs allow you to earn interest tax-free, they are one of the simplest ways to grow savings in the UK. Using the calculator can help you plan how much you need to save to reach a particular goal or compare the impact of different ISA interest rates.
What Does The Cash ISA Calculator Show?
The calculator estimates how your savings will grow based on the inputs you provide. It combines your deposit, contributions and interest rate to show an estimated final balance and the total interest earned.
This helps illustrate how compounding works. When interest is added to your account, future interest is calculated on the new higher balance, meaning your savings can grow faster the longer they remain invested.
The results give you a useful estimate of how much your savings could grow, but actual returns will depend on the interest rate offered by your provider and whether it changes over time.
Step 1: Enter Your Initial Deposit
Start by entering the amount you plan to deposit into your Cash ISA today. This is your starting balance.
You can enter any amount depending on how much you want to save. Some people start with a lump sum, while others begin with a small amount and add to it regularly.
If you don’t plan to start with a lump sum, you can simply enter £0 and rely on monthly contributions instead.
Step 2: Add Monthly Contributions
Next, enter how much you expect to save each month.
Regular contributions can make a significant difference to the long-term growth of your savings. By adding money each month, you increase the balance that earns interest, which helps your savings compound more quickly.
You can experiment with different contribution levels to see how increasing your monthly savings affects your final balance.
Step 3: Enter The Interest Rate (AER)
The interest rate determines how quickly your savings grow.
Most Cash ISA providers quote their rates as AER (Annual Equivalent Rate). This reflects the yearly interest rate including compounding.
By entering different rates into the calculator, you can see how choosing a higher-paying ISA could impact your returns over time.
Step 4: Choose The Time Period
Next, select how long you expect to keep your money in the Cash ISA.
The longer your savings remain invested, the greater the effect of compound interest. Even small balances can grow substantially if they are left untouched for many years.
This feature can help you plan savings goals such as building an emergency fund or saving for a future purchase.
Step 5: Review Your Estimated Returns
Once you’ve entered your details, the calculator will show your estimated results.
These typically include:
Your projected final balance
The total amount you contributed
The interest earned over time
This allows you to see how much of your final balance comes from your own contributions and how much comes from interest.
What The Results Mean
The results from the calculator are only estimates. They assume that the interest rate stays the same throughout the entire time period and that no withdrawals are made.
In reality, Cash ISA rates can change, especially for easy-access accounts. Some ISAs also offer temporary bonus rates that may expire after a certain period.
However, the calculator still provides a useful way to compare savings scenarios and understand how your money might grow over time.
How To Use The Calculator For Planning
The calculator is particularly useful for testing different savings strategies.
For example, you can:
Compare the effect of different ISA interest rates
See how increasing monthly savings changes your final balance
Estimate how long it could take to reach a savings target
Understand how compounding increases returns over time
Because Cash ISAs allow you to earn interest tax-free, they can be an efficient way to grow savings without paying tax on the interest earned.