Below I have attached my spread sheet which shows examples of how I would theoretically set up a day rate as a working free lance photographer. I feel as though these spreadsheets are quite self explanatory; you simply enter all the relevant information, whether that be about your photographic equipment, personal bills, business equipment, housing/living costs etc. Then from that you can calculate what you would need to charge people in order to cover all the costs of you and your business.
Here you can see that hypothetically I would need to charge £200 as my day rate, £120 as my half day rate and £75 for a 1-2 hour job. If I did charge this then technically I should be able to pay for everything I need to with no issues at all. However, as always business, especially photographic business, is not always steady and certain, so some months you may have a lot of jobs and other months you may not which means your income may change monthly. This is just something you should be aware of as a freelancer and also be prepared for as you may need to adjust your out going payments to fit in with your income.