The first calculation is obvious: net pay minus childcare and commuting.
The second calculation is easier to miss: employer pension, benefits, future salary progression, experience, confidence and the financial cost of a longer career gap.
Build two answers
NowNet pay, childcare, commuting, meals, clothing and household support.
LaterPension contributions, employer benefits, progression and future earning power.
LifeFlexibility, health, identity, care and what the family wants.
The immediate financial gain may be modest. The long-term value may be larger. Or the timing may simply not work for the family yet.
A complete calculation can still lead to either decision. Its job is clarity, not persuasion.