Start from your monthly budget and work backwards to the maximum loan and home price.
# What mortgage can I afford?
# Start from the monthly payment you are comfortable with and work backwards to the loan.
# Inputs
monthlyBudget = 1400 €
annualInterestRate = 3.8 %
loanTerm = 25 years
downPayment = 60000 €
# Monthly rate and number of payments
r = annualInterestRate / 12
n = loanTerm / (1 month)
# Reverse annuity: L = p * ((1+r)^n - 1) / (r * (1+r)^n)
maxLoan = monthlyBudget * ((1 + r)^n - 1) / (r * (1 + r)^n)
# Maximum home price you can aim for
maxHomePrice = maxLoan + downPayment
# Total you pay the bank
totalPaid = monthlyBudget * n
totalInterest = totalPaid - maxLoan
# What if interest rates rise by one point?
rHigh = (annualInterestRate + 1 %) / 12
maxLoanHigh = monthlyBudget * ((1 + rHigh)^n - 1) / (rHigh * (1 + rHigh)^n)
lossPerPoint = maxLoan - maxLoanHigh