Refurbished iPhone depreciation: measure a change without extrapolating

Choose two dates and a consistent scope

Calculate (final price − initial price) ÷ initial price × 100. A negative result describes a drop; a positive one describes an increase. State both dates, the model and the market. The worked example uses entry-price observations and cannot establish that storage, condition and seller were identical at both ends.

Do not turn weeks into a year

Multiplying a monthly change by twelve does not measure annual depreciation. A one-year comparison requires actual coverage and comparable observations. Until the series covers that period, we do not publish an observed annual rate. Even a full year's history does not predict the next year.

Separate retail from personal resale

A professional seller's entry price comes with that offer's conditions. It is not the amount a buyer or trade-in service will pay you. Obtain quotes for your device's storage, battery and condition, on the same date, rather than deducting an arbitrary percentage from a retail listing.

Calculate the cost of changing phones

Add known charges to the chosen phone's final price, then subtract the actual trade-in quote. That remainder is your replacement budget. A lower purchase price can be offset by a lower resale offer, so keep both amounts dated and distinguish estimates from guaranteed proceeds.

Give waiting a deadline

Decide what saving would justify waiting and the latest date you can buy. Use later readings to monitor that condition. A flat chart does not establish a permanent floor, and a previous drop does not establish that the movement will continue.