Einstein taught us that energy and matter are convertible with a cute little formula that I confess after several courses in college physics I don’t really understand. But as a metaphor I think I really get it.

When we work for money, we are converting our precious moments of time into units of financial wealth. There are a fortunate few who are independently wealthy and can live off their investments, and frankly I think that’s great. (I’m much more impressed if they earned that independence over their lifetime rather than inherited.) The rest of us schlubs need to think hard about this calculation: what is our free time worth?

There are plenty of activities that I really love, and I would never put a price on them. But often I need to think about trading off my time to do a chore vs. paying someone to do it for me. Home Depot offers to deliver a Christmas tree to your door this year. Or you could pay less and go pick it up yourself. Lawn care specialists will gladly come to your yard, fertilize, aerate, plant, and weed for a fee. I’m tempted by the thought of a cleaning specialist (who in my mind looks exactly like Marry Poppins) who will scrub and tidy my house top to bottom. But lazybones here could do it myself.

Should I? What is my time worth?

I’ve seen a few ways to calculate this, but I choose a simple path. Add up all your sources of income in a given year: salary, interest income, bonuses and dividends if any, etc. Take out taxes (estimating is fine in my book). The result is your yearly take-home income.

Adding up all our waking hours (since paid or not, you can’t do much while asleep), that’s 6570 hours a year.

Divide your take-home annual income by 6570, and that figure is what your waking time is worth, per hour.

My number is in the low double digits (and less than I thought!) but let’s see if it will help me decide whether trading my money for services is worth it, or whether I should just do it myself.

Normally I buy a 7 foot Christmas tree, usually at Home Depot, for about $70 with tax. The staff person there straps it to the roof of my car, and I tip him $10. So that’s $80 for a do-it-yourself Christmas tree purchase and delivery.

Through their direct marketing email today, I learn that Home Depot will deliver to me a fresh cut 7 foot tree (with stand, although I already own one) for $114, plus $34.13 shipping charge, plus $8.89 state sales tax. That’s about $157.

$157 — $80 = $77. That’s WAY more than my hourly “free time” value. So unless I’m incredibly lazy this December, or physically incapacitated in some way, it makes no sense to buy the fresh tree online and have it delivered. I’m willing to trade about an hour of my life to drive over, pick it out (which is fun with my niece in tow, anyway), strap it on, drive home, and unload, to save $77.

It’s also cheaper, in the time/value equation, for me to take care of my own lawn rather than hire Scotts LawnService (dammit!). But hey”another advertisement I just received quoted me a great hourly rate for professional home cleaning , and it’s less than the value of my hourly free time. So if I hire a maid, I’m spending a small amount of money but buying a lot of free time. This sounds promising!