Calculateur du Seuil de Rentabilité

def break_even_units(fixed_costs, price_per_unit, variable_cost_per_unit):
    """Calculate break-even quantity in units."""
    contribution_margin = price_per_unit - variable_cost_per_unit
    if contribution_margin <= 0:
        raise ValueError("Price must exceed variable cost per unit.")
    return fixed_costs / contribution_margin

def break_even_revenue(fixed_costs, price_per_unit, variable_cost_per_unit):
    """Calculate break-even revenue."""
    cm_ratio = (price_per_unit - variable_cost_per_unit) / price_per_unit
    return fixed_costs / cm_ratio

def margin_of_safety(actual_revenue, break_even_rev):
    """How far sales can drop before hitting break-even (as %)."""
    return (actual_revenue - break_even_rev) / actual_revenue * 100

# Example: coffee shop
fixed_costs  = 5000   # monthly rent, salaries, etc.
price        = 4.00   # per cup
variable     = 1.20   # per cup (coffee, milk, cup)

units = break_even_units(fixed_costs, price, variable)
rev   = break_even_revenue(fixed_costs, price, variable)

print(f"Break-even units:    {units:.0f} cups/month")
print(f"Break-even revenue:  ${rev:,.2f}/month")

# Margin of safety if selling 2500 cups/month
actual_rev = 2500 * price
mos = margin_of_safety(actual_rev, rev)
print(f"Margin of safety:    {mos:.1f}%")