It’s 8:00 am, on my birthday, and I’m on a plane to Cincinnati. On the heels of several days of early wake-ups and late nights, I found myself uncommonly confused when the alarm went off at 4:45 this morning, and my husband David had to rouse enough to remind me that yes, that ring was intentional—and its intention was for me. He rolled back over after mumbling a sincere “happy birthday,” and I headed for the shower.

On the plane, my thoughts drift with the air currents beneath us and I begin to calculate, measure, assess, for at least the seventh time this week, my time away due to work and where it leaves me in the balance sheet of mommyhood this week. It goes something like this: made it home by 8:00 pm Monday night, though expected to be home after 10:00; thus had 45 minutes with Hannah before her bedtime, which is less than a typical weeknight– but more than I had anticipated. Same with Tuesday.

Wednesday, had to be up at 4:45 for a TV satellite tour so no morning time with her at all (though perhaps minimally offset by being able to tell her later that I took a picture of her and got it on TV with me)? Thursday—that’s today. Thankfully for her, she was not up to greet me at 4:45, but all the same, it was another morning of no time together—another mark in the deficit column (possibly given double negative points for the birthday factor depending upon one’s abacus). However, I deliberately took this early morning flight today instead of taking the more civilized route my colleagues preferred by going last night, to give me a good almost-two-hours of togetherness at home the previous evening. Ah, but then there’s the big red “x” in my head for tonight—the overnight stay— yet if Delta does its job I will actually be home by 5:00 tomorrow, at least an hour earlier than a typical work night evening arrival…

Beep, beep, Click, click, click, ca-ching… and the balance of this hefty algebraic equation is?

I have no idea.

All I know is that the calculations run like a continuously churning spreadsheet in my head, adding and too often subtracting. (Who knew this was where those trying honors math classes would find their ultimate application)? Though I realize now, the one course in mathematics for which no academic institution could have provided adequate preparation is this strange subspecialty that might be called “working mom math.” Skilled practitioners like myself have advanced dual degrees in motherhood and career, with a demanding minor in guilt.

In the constant computing, there are those occasional epiphany moments when it seems like the tally is in your favor. An unexpected windfall of a meeting that ends early, an evening that is laptop-free. But because that internal calculator never turns off, even then it’s hard not to measure its value (and your role in making it valuable). Is it still true quality time if, after all that hustling for extra home minutes, you spend it merely sitting side-by-side on the sofa while your child succumbs to the irresistible lure of a DVD? Does that still count? As much? Or what about on a blessed weekend day, if you were to go off to, say, get a haircut, or run errands uninterrupted, or (gasp) meet a girlfriend for a coffee—what about THAT?

I admire (and perhaps slightly envy) the mothers who cannot add—or have the higher wisdom to simply choose not to.

As I expect I shall never be one of them, I’ll simply take solace in the fact that through all this addition I should be getting really good at balancing my checkbook any day now. More importantly, I remind myself of this supreme truth about equations that any good mathematician knows: a sum can be greater than any of its parts.

And perhaps the textbooks should add this deserving corollary: when each of the parts are great, they can matter more than the sum.