Google's "weird" billing is due to automatic charges triggered by hitting a payment threshold, not a consistent monthly budget, and a 30.4-day billing cycle. When you reach this set spending limit or reach the end of the 30.4-day cycle (whichever comes first), Google charges your payment method to zero out the balance and restart the cycle. 
    This allows Google to minimize non-payment risks while providing flexibility for advertisers.
    Why You Get Charged at Different Times
    • Payment Thresholds:
      Instead of charging you per click, Google charges your account when your accumulated ad spend hits a predetermined payment threshold.
    • Dynamic Thresholds:
      Google may adjust these thresholds over time based on your account activity, leading to charges of different amounts.
    • 30.4-Day Cycle:
      If your spend doesn't reach the threshold within 30.4 days, Google will charge you on the first of the month or after the 30.4-day period, whichever occurs first.
    • Budget vs. Threshold:
      Your actual charges don't always match your stated monthly budget because the budget is a daily average, not a strict monthly limit, and the threshold determines when a charge occurs.
    How to Understand Your Charges
    • Check Your Billing Summary:
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      This section in your Google Ads account shows your spending, upcoming charges, and when they will occur.
    • Review Invoices:
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      You can find invoices and receipts for past charges in the "Documents" section of your billing summary.