Since this formula's own guarantee is calculated from your original purchase date, your order confirmation email is worth keeping accessible from day one.
Your order number, the purchase date, the exact package and price you paid, and any correspondence with customer support — all worth keeping in one place, not just your inbox.
Since this formula's own materials describe daily comfort building gradually over several weeks of consistent use, having your purchase date clearly documented protects you across the full 60-day guarantee window.