US online retail sales growth has slowed for four consecutive quarters YoY for the first time since 2012, according to FTI Consulting’s “2019 US Online Retail Forecast.”

The findings suggest that online retail sales may have reached an inflection point, if for no other reason than its underlying size. In the most recent four quarters, growth of online sales has slowed to 13.3 percent from 16.1 percent a year earlier, and has decreased even further to the low 12 percent range in the two most recent quarters.

FTI expects US online retail sales will be $575 billion in 2019, a 12.3 percent increase over $513 billion in 2018. The numbers, however, are low compared to the 14.2 percent increase in 2018 where the market topped $500 billion for the first time. The company predicts the figure will reach $645 billion in 2020, a 12.1 percent increase and $1 trillion by late 2025.

Despite the deceleration of online spending growth, the e-commerce channel captured nearly 43 percent of total retail sales growth in 2018, the report notes. By 2025, online retail sales will hold a market share of total retail sales of 21 percent compared to 15 percent in 2019.

While no single event can explain shoppers’ spending slowdown, the report cites negative developments in 2018 such as the government shutdown and escalation of trade tensions.

“For omni-channel retailers, recognizing an inflection point for their product categories should impact business planning decisions. Failing to do so could result in over-investment in costly online expansion projects, such as distribution centers and logistics support, under a potentially erroneous assumption that high growth rates are sustainable for a prolonged period,” said Christa Hart, a senior managing director in the Retail & Consumer Products practice at FTI Consulting.

Though it recently launched its fifth Prime Day and reported $14 billion in Prime subscription fees in 2018, Amazon may also experience its own limit as its retail sales growth slowed notably in recent quarters. FTI forecasts the giant’s retail sales growth rate to slow to 19 percent in 2019 from 30 percent in 2018.

“While a slowdown in online sales growth will impact the channel as a whole, it may matter less for established online leaders, such as Amazon and Wal-Mart, as they focus their efforts on getting existing customers to spend more with them,” noted said J.D. Wichser, leader of the Retail & Consumer Products practice at FTI Consulting.