Idaho local data guide

How Holding Costs Impact the 70% Rule for House Flips in Idaho

For real estate investors in Idaho, the 70% rule serves as a fundamental screening tool to estimate the Maximum Allowable Offer (MAO) on a property. The rule stipulates that an investor should pay no more than 70% of the After Repair Value (ARV) minus repair costs. The remaining 30% acts as a critical buffer, not profit, intended to cover selling costs, commissions, and all holding costs. Because holding costs accrue daily, delays in project timelines directly erode this buffer, often making the difference between a profitable flip and a financial loss.

Updated with grounded research as of 2026-10-06.

The short answer

Holding costs function as a 'leak' in the 70% rule's 30% buffer. In the Idaho market, where property taxes, insurance, and utilities are ongoing monthly expenses, every day your project exceeds its planned timeline, these costs accumulate. Because the 70% rule is a static formula, it does not automatically scale with time-based expenses. If your renovation takes longer than estimated, those additional days of hard money interest, taxes, and utility bills are paid directly out of your projected profit margin, essentially shrinking the 30% buffer you set aside to handle unforeseen project costs.

Key facts

70% Rule Formula
Maximum Allowable Offer (MAO) = (ARV × 0.70) – Repair Costs
The 30% Buffer Composition
The 30% margin is not pure profit; it must cover closing costs, agent commissions, holding costs (taxes, insurance, utilities, financing interest), and the desired profit.
Idaho Holding Cost Variables
Holding costs vary by county and municipality in Idaho, influenced by local property tax levies, specific utility providers (e.g., Idaho Power or local water districts), and current interest rates for hard money loans.

The Anatomy of Holding Costs

Holding costs are the 'carrying costs' required to own a property while it is being renovated. They are time-dependent expenses that continue regardless of whether construction is active or stalled.

  • Financing: Interest payments on hard money or bridge loans often carry high monthly rates.
  • Taxes: Property taxes in Idaho are due biannually, but should be accrued monthly for budgeting purposes.
  • Utilities: Monthly minimums for electricity, water, gas, and sewer continue even if the home is vacant.
  • Insurance: Vacant property insurance is typically more expensive than standard homeowner policies.

Why the 70% Rule Often Fails to Predict Holding Costs

The 70% rule is a high-level screening tool, not a precise underwriting model. It assumes a standard duration for renovations. When projects face delays—such as permitting hold-ups with local Idaho building departments or material shortages—holding costs balloon while the ARV stays fixed.

  • Overpayment Risk: Relying solely on the rule without accounting for local Idaho market timelines can lead to overpaying.
  • Buffer Erosion: Every week of delay removes a specific dollar amount from your 30% buffer, reducing the project's safety net.
  • Market Sensitivity: In competitive Idaho markets like Boise or Coeur d'Alene, the temptation to rush or overpay for a deal often leads investors to underestimate holding time.

Strategies for Idaho Investors

To use the 70% rule effectively in Idaho, investors must stress-test their numbers against varying time horizons.

  • Run a Best/Worst Case Scenario: Calculate holding costs for your projected timeline, then add a 30-day 'buffer' period for unexpected delays.
  • Localize Costs: Research property tax rates in the specific Idaho county and obtain accurate quotes for utilities and vacant home insurance before making an offer.
  • Adjust the Buffer: If the project is complex or in a slow-permitting area, consider using a 65% rule instead to increase your margin of safety.

Common questions

Is the 30% buffer in the 70% rule meant to be pure profit?

No. The 30% buffer is intended to cover all transactional costs, selling commissions, holding costs, and profit. If you treat the entire 30% as profit, you will likely encounter cash flow issues when unexpected holding costs arise.

How do Idaho property taxes impact my holding cost estimate?

Idaho property taxes vary significantly by county and city. You should use the specific tax levy for your property's location (often found via the County Assessor's website) and divide the annual estimate by 12 to include it in your monthly holding cost budget.

Related Idaho questions

  • What are the typical monthly holding costs for a single-family home in Idaho?
  • How do I estimate an accurate after-repair value (ARV) for properties in the Boise metro area?
  • Should I adjust the 70% rule if market conditions in my Idaho city are highly competitive?

Sources and verification