@Jill Hutson, vacancy and turnover costs are EXPENSIVE especially if you are an out of town landlord paying an agent/PM for tenant placement.
Here are some things I think about with regard to this issue.
1. Market rent: I don't look at market rent as 1 single number that I want to meet or exceed. Quite the opposite. I think of it as a range of rental prices of comparable properties and my goal is to make a good return on the lower end of that range of values.
For example, if you identify market rent for a unit as $3,000, I might be thinking of it has $2,600-$3,400. I might want to rent my unit out for $2,650-2,700 if I can make a decent return at that.
2. I think carefully about the value proposition I am offering a tenant. I look for opportunities to offer MORE for a tenant but I look for low hanging fruit in this regard. What is this property best suited to offer.
For example, the layout of one kitchen might lend itself to adding a dishwasher easily. Another house might be a single family home with a fenced yard and LVP flooring and be more suitable for allowing pets.
3. By offering a BETTER value proposition at a lower than average price a tenant is VERY hard pressed to have a motivation to move and to be able to find a comparable property for similar rent.
So, if I budget 5% for vacancy, I can readily beat that budgeted estimate.
4. My cash-flow is NOT affected by vacancy! That sounds crazy, I know but it depends on how you view cash-flow. I view it as the money I can pay myself. So, I don't just factor in hard expenses like mortgages, taxes, insurance, utilities. I also factor in soft budgeted expenses like cap ex, maintenance, and vacancy.
For example, if I had a $3k rental and the hard expenses were $2,200 you might view this as $800 cash-flow positive, but I am going to budget maybe 15% for those soft expenses and my cash-flow would be $350 per month. The difference is that as long as I am managing those soft expenses well my number is solid and consistent. With your estimate, you might earn $800/month for 2 years and then incur a vacancy at the same time as you need a roof replacement and for that tax year your cash-flow might be -$1,200/month.
I prefer my method because with the $800/month estimate you might buy a property believing its a great deal, BUT sell it after several years having made negative cash-flow. I view the soft expenses as things that WILL happen and so the money is accounted for when its received even though it isn't spend on a monthly basis much like how taxes and insurance are often escrowed.
5. If I was going to improve on one thing, I could certainly tighten up my turnover process and make units ready to rent again a little faster or even advertise a little ahead of when they are ready. I might be able to lessen my average turnover time from ~5 weeks to maybe ~4 weeks. I have no intention of showing properties before they are vacant at this time. So, I can't see reducing it further.