If you are referring to the classic 70% repairs, here is some insight I hope is helpful.
This is a general rule to start at, and used for average priced homes.
You take the ARV of the house and multiply it by 70%. This is is to give you a 30% spread for your holding cost, selling cost, money cost, and profit. Then you subtract the repairs. This gives you your MOA.
Example: House ARV: 100K, Repairs: 25K, MOA: $45,000
100,000*70%= $70,000
70,000-25,000= $45,000
Now when you are looking at homes that are more expensive (450K+) you may not need to use the whole 70% because the cost of your money won't change depending on the price of the house.
This is just a baseline guide, similar to any of the other "rules". It depends on the house, location, market information, rental rate and amount of repairs. There are other factors that could go into play as well.
Feel free to reach out if I can be of more assistance :)
Good luck!