The best way to calculate your offer is to work with a realtor to try to estimate the 'after fix up value' of the home, what will it be worth AFTER you do the repairs? Then, subtract the cost of the repairs (all of them, even the minor fixes), then subtract a reasonable percentage as compensation for your time and trouble. That is your highest and best offer. Most investors will insist on 30%, if you intend to occupy the home, you may be willing to accept 25% or even 20% as 'sweat equity' compensation. It's entirely up to you, but don't try to base your offer on anything other than hard numbers and facts and be ready to back it up with written estimates, comparable sales, and so on.