so I found this super-neat and mathtational online freelance-hourly-rate-calculator (via swissmiss).
It asks you to enter in all of your yearly costs, both personal and business, your desired work/vacation schedule and how much of a profit you’d like to make, and then let’s you know what you would need to charge per hour to make that happen.
MY IMAGINARY LIFE SCENARIO: Freelance Trampoline-Tester

BUSINESS COSTS/YEAR:
How much is your annual Office Rent? $48,000: for a warehouse in queens with 26ft ceiling (for maximum bounce-capacity).
How much do you spend annually on Travel? $5,000: a few business trips to trampoline expo’s I imagine.
How much do you spend each year on Software? $0: pshah.
How much do you spend each year on Communications? $1200: internet + cell phone + handsfree ear piece, so I can conference call mid-air.
How much does your annual Insurance cost? $10,000: totally making this up, but I imagine trampoline-testing might require ample insurance…
How much do you need to spend on Legal Fees? $0: nothing says “oooh, great idea! no really.” like deciding to represent yourself.
How much do you need to spend on Accountancy Fees? blablabla boring question, next.
How much will your Office Supplies cost annually? $2350 = $350 (several pairs of skid-resistant jumping socks) + $2000 (knee pads/helmet/mouthguard/parachute), because Safety First.
How much will you be spending on Advertising and Promotions? $22,500 (for 5 sky-writing campaigns at $4,500 per flight).
PERSONAL COSTS/YEAR:
How much is your annual Rent / Mortgage payments? $16,000 = $10,000 to build my treehouse (I found a tree house construction company in philly) + $6000/year (a guess on what someone might charge me to rent their backyard tree in NYC at $500/month)
What is your annual budget for Daily Expenses? $20,000 = since it is probable that I will not have electricity in my tree house, and since fire+trees=no-good, I will be dining exclusively on food thats require no refrigeration and no cooking, and takeout. so let’s say $10,000 on food + $10,000 for other-important-life-stuffs, like ships-in-bottles and the like.
How much do you intend to save for your Retirement Account? $15,000 (hey, why not?)
How much do you spend each year on Occasional Expenses? $13,500 In this imaginary life, I’ll obviously want to take taxidermy classes (Here they cost $3500) + I will take a month long vacation to the Canary Islands (approx. $10,000).
WORK SCHEDULE
How many days a week do you work on average? 4 days. when you work for yourself you create your own schedule, gosh darn it.
How many days of vacation do you need annually? 30 days. (for the canary islands trip)
How many sick and personal days do you need annually? 20 days (just in case I fall out of the tree house, or get a heart attack from eating only take-out)
How many public and religious holidays? 31 days (though no religious holidays will be observed, I will take an entire month off to celebrate Bastille Day.)
How many hours do you work a day on average? 7 hours (4 hours bouncing, 1 hour lunching, and 2 hours administrating)
Approximately what percentage of hours can you actually bill? 85%
Enter a Dollar amount of Savings/Profit you’d like to make each year Profit is the money above what it costs just to run your business and live, what extra cash do you wish to earn: $1,000,000 (listen here, buster, I’ve been working for non-profits all this time, allow me this one imaginary moment of corporate greed!)
AND FINALLY,
To live this magical life, I would need to charge a mere $1533.18 p/hr. Easy.