ISA / TFSA Tax-Free Account Comparison Calculator
Compare tax-free vs taxable account returns
Enter your annual contribution, time horizon, expected return, and tax rate to see how much more a tax-sheltered account like an ISA or TFSA can grow compared to a regular taxable account.
Why a Tax-Free Savings Account Can Transform Your Long-Term Wealth
Tax-sheltered investment accounts are among the most powerful tools available to ordinary savers. Whether it is called an ISA in the United Kingdom, a TFSA in Canada, or a Roth account in the United States, the core principle is the same: your investment grows without being eroded by tax on dividends, interest, or capital gains each year. Over a long enough time horizon, this compounding advantage can add tens of thousands of dollars to your net wealth.
When you invest in a standard taxable brokerage account, your returns are reduced each year by taxes on income and gains. If you earn a 7% annual return but pay 25% tax on investment income, your effective after-tax return drops to around 5.25%. That reduction compounds negatively over decades. A dollar growing at 7% for 30 years becomes roughly $7.61. At 5.25%, the same dollar reaches only about $4.54. That difference is entirely the cost of tax drag.
In a tax-free account, you keep the full 7% return each year. This calculator models exactly that difference. The taxable account calculation uses an after-tax return rate equal to the gross return multiplied by one minus the tax rate. Then, upon withdrawal, any remaining gain above total contributions is taxed again. This double-layer approach reflects how capital gains are often treated in practice.
ISA vs TFSA: Similar Goals, Different Rules
The UK Stocks and Shares ISA allows individuals to invest up to 20,000 pounds per tax year with all growth and income completely tax-free. There is no tax on withdrawal and no requirement to report the account on your tax return. The ISA has been available since 1999 and has helped millions of British savers build substantial wealth without the friction of annual tax reporting on investment returns.
Canada's Tax-Free Savings Account, introduced in 2009, works similarly. Contributions are made with after-tax dollars and the account accumulates room each year (currently $7,000 per year as of 2024). Unlike a Roth IRA, withdrawals from a TFSA restore your contribution room in the following year, adding extra flexibility for short-term saving goals as well as long-term ones.
In the United States, the closest equivalents are the Roth IRA and the Health Savings Account (HSA). The HSA is arguably even more powerful for those who qualify, offering a triple tax advantage: deductible contributions, tax-free growth, and tax-free withdrawals for qualified medical expenses.
Maximizing the Tax-Free Advantage
The key to getting the most from a tax-free account is to fill it with your highest-returning, most tax-inefficient assets. Assets that generate frequent dividends or interest income are ideal candidates for sheltering, since those distributions would otherwise be taxable every year. Index funds tracking broad markets work very well in these accounts because of their growth profile and low turnover.
It is also important to contribute consistently and early. The compounding advantage of a tax-free account is time-dependent. If you are 25 years old and you contribute $10,000 per year for 35 years at a 7% return, the tax-free account produces more than $1.38 million by age 60. A taxable account at the same gross return but after a 25% tax drag on returns might yield significantly less depending on how gains are taxed at withdrawal.
This calculator provides a clear side-by-side view so you can input your specific numbers and see the real monetary advantage of using your available tax-free allowance every year. Even if you cannot max out your allowance, sheltering as much as possible within your budget is almost always worthwhile. The opportunity cost of leaving a tax-free account unfilled grows larger with every year that passes.
