Hi,

You can use compute and inverse method to achieve this.

Example:

percentage = fields.Float()
percentage_inc = fields.Float(compute='_compute_percentage_inc', inverse='_inverse_percentage_inc', store=True)

@api.depends('percentage')
def _compute_percentage_inc(self):
    for rec in self:
        value = 500
        rec.percentage_inc = (value * rec.percentage) / 100

def _inverse_percentage_inc(self):
    for rec in self:
        value = 500        
        rec.percentage = (rec.percentage_inc / value) * 100

Consider value as your stored value on which percentage computed
Inverse function will execute on saving the record

Regards