WASHINGTON

Every month, Tanita Alfaro, a diminutive night-shift office cleaner in Rockville, Md., puts aside $150 to send to her parents in an impoverished village near the Salvadoran city of San Miguel. Her husband walked 1,700 miles from their war-torn land to the United States-Mexico border 25 years ago and, several years later, she followed.

Ms. Alfaro apportions the money “right away, payday, before I buy so much as a stick of gum” — before she manages the budget that feeds their three young children. For her parents, it is a lifeline. “Between my brothers and me — all of us here, working hard — we keep them alive,” she told me. “We pay our parents’ rent, food, medicines. Everything.”

It’s a scenario immigrants know well. Last year, according to the World Bank, migrants sent $401 billion to their families in developing countries. That’s eight times the United States’ budget for foreign aid, including military and economic assistance. It’s roughly equivalent to the gross domestic product of Austria or South Africa. By 2015, the number could rise to $515 billion.

For India or China, which together receive nearly a third of the remittances, the cash flows have a negligible impact on their burgeoning economies.