Not by taking a percentage off the asking price. The asking price is an opinion; comparable sales are evidence.
The foundation is recent sales of genuinely similar homes nearby — sold prices, not asking prices. Similar means comparable in type, size, age, condition and situation. Recency matters: in a moving market, sales more than about three months old need interpreting rather than accepting.
No two homes are identical, so each comparable is adjusted toward the subject property — for finished basement, garage, lot size and position, condition and updates, and outlook. A comparable that sold for $700,000 but backs a busy road while your subject backs green space is not telling you the subject is worth $700,000.
The same evidence supports a different offer depending on whether homes in that segment are selling above asking in days or sitting for months. Sales-to-new-listings and months of supply describe that. Live figures →
How long it has been listed, whether it has been reduced or relisted, whether a previous deal collapsed, how motivated the seller appears, and whether anyone else is writing. This is where listing history matters and where a public portal tells you nothing. Reading motivation →
The output is not a single number. It is a range — what the evidence supports, what it would still be reasonable to pay, and the point past which you are buying someone else's optimism.