A bit every month. What did it become?

Why they land apart

Tax on dividends. When a fund based in the US, like SPY, VOO or QQQ, pays dividends to someone who is not a US citizen or resident, the US generally keeps 30%. If their country has a tax treaty with the US, that usually drops, often to 15%. US residents have nothing kept back at this point, though they pay their own income tax on it later. A fund based in Ireland, like CSPX or CNDX, generally has 15% taken off inside the fund instead, whoever owns it, under the US and Ireland tax treaty. That is why Irish funds come out ahead mainly for people in countries with no US treaty. Over many years the gap adds up.

The yearly fee. Each fund takes a small slice every year to run itself. It is already inside the price, so you never see a bill.

Paid out or kept in. Funds that pay dividends out leave you to reinvest them yourself. Our sums assume you did, every month, after tax. Funds that keep them in do it for you.

One more for US-based funds. If you are not a US citizen or resident, US estate tax can apply when you die holding more than US$60,000 of US assets, and shares in a US-based fund count. Some countries have an estate tax treaty with the US that changes this. Shares in an Irish-based fund generally do not count. The IRS explains the US$60,000 rule, and our CSPX guide covers the detail.

Two indexes, two personalities

The S&P 500 is a list of about 500 large US companies across every industry: banks, shops, drug makers, oil and tech.

The Nasdaq 100 is the 100 largest companies on the Nasdaq exchange, leaving out banks and other financial firms. It leans much harder into tech. Start the Nasdaq 100 in March 1999 and look at the scary bit: the swings are bigger both ways.

How the sum works

Each month, we spend your amount at that month’s closing price and count the units you would own. Then we value them all at the latest price, on 9 October 2026.

For the S&P 500, the big number uses the index itself from January 1988, with all dividends reinvested and no fees or tax. For the Nasdaq 100 we use QQQ from March 1999, the oldest fund that copies it, with dividends reinvested. QQQ’s prices already have its yearly fee taken out (0.18% today), so for the Nasdaq 100 the funds below are compared with a fund, not the bare index. The fund list uses each fund’s real prices, with dividends from US-based funds cut by the rate for the country you pick, then reinvested that month.

What it leaves out

• Broker fees. Commissions are not taken off. On small monthly amounts a fixed fee can eat a big share, so check your broker’s charges.
• Your own currency. Everything here is in US dollars. If you spend pounds, euros, rupees or anything else, your result in that currency also depends on the exchange rate over the years. For Singapore and Australia, our Singapore and Australia versions do that for you.
• Whole units. Some funds cost hundreds of US dollars a unit. The sums assume you can buy part of one. If your broker only sells whole units, you would save up and buy one every few months instead.
• Tax where you live. Many countries also tax dividends or gains. Only the tax the US keeps back is counted here.
• The future. These are past prices. The next 20 years could be better, worse, or very different.

This is general information to help you understand how index investing works. It is not advice to buy any fund.