Common mistakes include entering the wrong deposit, property price or mortgage term, and forgetting that a larger deposit may affect the loan-to-value band and available rates. Many calculators show a simple repayment estimate, so check whether it includes fees, insurance, taxes and other costs, and remember that rates can change. Do not assume the result is an affordability decision, as lenders also assess income, spending, debts and credit history. For a more accurate picture, compare figures from FCA-authorised lenders or speak to a regulated mortgage adviser.