In my case I also paid a premium on top of the rent over the next 18 months which accrued to be my downpayment on the property at the time the lease option was exercised.

Outstanding Account Balance: will accrue at 18% annual percentage rate effective immediately upon move-out and return of possession to Landlord.

Do you just plan for those numbers in your analysis but then take it all as "cash flow" and pay it as it comes up, or do you actually accrue those dollars in an account?

@Mike Sherman, technically it is 12% per annum, which should be calculated on a per diem basis. 12% per annum on $1,000 works out to interest accruing at the rate of 32.8767 cents per day. 

The other liens I have are currently still accruing interest.

The house at that point would be cash flowing $68 a month as well as accruing equity for as long as we have it.

For flip property, whatever you spend directly on the property is accrued and becomes part of the "Cost of Goods Sold" when you complete the flip.Whether a nail gun is part of the Cost of Goods Sold, a deductible business expense, or a capital expense depends upon the specific circumstances unique to your situation. 

Why would you not want to accrue an amount of money for capital expenditures in your monthly operating costs? 

(Note: this exclusion applies to the gains accrued from an investment in an Opportunity Fund, not the original gains).

You will continue to accrue cash through rentals.