What if interest rates rise: a mortgage payment's sensitivity

payment[principal_, rate_, months_] := principal (rate/12)/(1 - (1 + rate/12)^(-months))

current = N[payment[400000, 0.065, 360]]

2528.272093971862

N[payment[400000, 0.08, 360]] - current

406.7862015456485

perPercentagePoint = N[D[payment[400000, r, 360], r] /. r -> 0.065]/100

263.0602719400421

Plot[payment[400000, r, 360], {r, 0.03, 0.10}]

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