For ASX investors looking to build an ultimate retirement portfolio, it's the dividends that are going to be the key factor when deciding on a potential investment.
You've got your classic dividend stocks that most investors will consider, such as Westpac Banking Corp (ASX: WBC), Telstra Group Ltd (ASX: TLS) and BHP Group Ltd (ASX: BHP). But I think many investors looking to build the ultimate retirement portfolio would be more partial to monthly dividend payers.
Retirees obviously need a good source of passive income, delivered regularly and reliably. That's why I think these two monthly ASX dividend payers are well worth a look for those trying to build a solid retirement portfolio.

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Ultimate retirement portfolio: 2 ASX dividend stocks that pay income monthly
First off, let's start with an exchange-traded fund (ETF). The BetaShares S&P Australian Shares High Yield ETF (ASX: HYLD) is an ETF that is specifically designed to provide high levels of franked dividend income to ASX investors. It does this by holding an underlying portfolio filled with top ASX dividend shares. At the most recent numbers, these included Rio Tinto Ltd (ASX: RIO), ANZ Group Holdings Ltd (ASX: ANZ), Macquarie Group Ltd (ASX: MQG) and Transurban Group (ASX: TCL), amongst many others.
HYLD uses this portfolio to fund monthly dividends for its investors. This does tend to fluctuate. However, as of 31 March, the provider told investors that HYLD was trading on a trailing dividend yield of about 4.2%. Like any income stock, there is no guarantee that this will continue or increase going forward, of course. But given the quality of HYLD's underlying portfolio, I think this is a great stock to consider for the ultimate retirement portfolio.
Next up, let's talk about Plato Income Maximiser Ltd (ASX: PL8). Plato is a listed investment company (LIC), meaning that, similar to an ETF, it holds an underlying portfolio of investments that it manages on behalf of its shareholders. Unlike an ETF, though, Plato has far more discretion over its dividend payments, which it tends to keep consistent over time.
Plato's portfolio holds many of the companies that can be found in HYLD, including BHP, ANZ and Telstra. It also currently features Coles Group Ltd (ASX: COL), Medibank Private Ltd (ASX: MPL) and Woodside Energy Group Ltd (ASX: WDS).
Plato also pays out monthly dividends, which tend to come fully franked as a bonus. At recent pricing, this ASX dividend stock was trading on a healthy yield of about 4.85%.