Summer’s most glorious days lie in the weeks between Memorial Day and Labor Day (at least here in the United States). Technically, summer lingers until September 23, but we all know once those Labor Day barbecues wane, it’s time to pack up the beach umbrellas and head back to regular life.

But wait! Does it seem like you’ve squeezed in a little more barbecuing this year? You’re not imagining things. Time-dilated summer is real. It’s a trick of the calendar; this year, Memorial Day—the last Monday in May—fell on its earliest date, and Labor Day—the first Monday in September—will be on its latest date. The combination of the two means summer this year is 15 weeks instead of the usual 14.

The last extend-o summer was 2009. The next will be 2020. We made a handy chart for reference [below].

Knowing the week before Labor Day is a freebie makes these last popsicle days all the sweeter.

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Each dot here represents a day, starting with May 1 each year. The days that fall between Memorial Day and Labor Day are in yellow, rather than green. In some years, highlighted in gray, the two milestones capture an extra seven days. And 2015 is one of those magical years.