Every month I invest a set amount of money into my retirement account to build up my stock portfolio regardless of market conditions. As the saying goes, it's not about timing the market, but rather your time in the market.

Over the past 20 years, a $10,000 investment in a buy-and-forget S&P 500 index fund would have turned into more than $35,800, with 6.5% annual growth year after year. However, had you missed just the market's best-performing 20 days over those two decades, you would have made virtually nothing, and you would have lost money if you'd missed more days.

So next month when I make my next investment, I'll be buying Lowe's (LOW -0.49%) and Procter & Gamble (PG -0.13%), and then I'll promptly forget about them (well, not really, but you get my meaning). Here's why I'll be buying these two stocks in particular.

Two men with grocery bags in kitchen

Image source: Getty Images.

1. Lowe's

Home center giant Lowe's just reported earnings that trounced Wall Street's expectations, posting sales of $24.4 billion, which generated $3.21 per share in profits. Analysts had forecast the DIY center would earn $2.59 per share on $23.8 billion in sales.

I love that Lowe's stock is dropping 3% on the news and wish I was putting money in today. While that's a good argument for always keeping some money free to take advantage of situations like this, I'll still be buying regardless of whether its stock is higher or lower at the time.

Some speculate investors are taking profits on Lowe's stock (and that of Home Depot too, which is also trading lower after reporting strong earnings), or perhaps it's because of recent housing market reports.

Housing starts plummeted 9.5% in April, likely due to the lumber shortage that is causing the price of lumber to skyrocket. At the same time, existing homes sales also fell to a seven-month low as the inventory of available homes dries up. With fewer homes being built or bought, there is less need for all the supplies and furnishings to make them livable. 

Yet this is not like the housing market crash during the Great Recession, but rather a pandemic-fueled hiccup that will soon sort itself out. With interest rates being kept artificially low, demand will stay put while rising prices will induce homeowners to put their homes up for sale. The housing bull market will continue charging higher, bringing Lowe's right along with it.

Better still, Lowe's has a long history of paying a dividend and a strong record of raising the payout each year. For nearly 60 years the DIY center has raised its dividend payment, which currently yields a modest 1.25%, putting it in the group of stocks known as Dividend Kings. I'll be adding this bit of royalty to my portfolio next month.

2. Procter & Gamble

Similarly, Procter & Gamble has a long rich history of paying shareholders dividends (some 130 years!). Like Lowe's, it has also increased the payout annually for over 50 years, also making it a Dividend King.

The longevity of its business, though, means it has been through all kinds of market conditions -- recessions and depressions, war, calamity, and boom times, too -- and has not only survived them all, but thrived.

What has made that possible is the incredible portfolio of consumer name brand products that you'll likely find at least one of in your own home. From Crest toothpaste and Tide laundry detergent to Pampers diapers and Old Spice deodorant, its products cover the gamut of necessities in the kitchen, bathroom, and laundry room that are used every day, and hold the No. 1 or No. 2 spot in those categories. 

It's also a global powerhouse, with 56% of its annual sales actually coming from international markets -- though the U.S., with 44% of its sales, is the single largest market for P&G. Yet Crest and the Oral-B brand of oral care products helped it have the second largest share globally, with nearly 20% of the market.

The pandemic showed just how crucial its brands are to consumers. Over the first nine months of Procter & Gamble's fiscal year, sales are up over 7% to more than $57 billion while profits are 12% higher.

The consumer products giant is a stable staple of households everywhere, and that is why it will be added to my portfolio.