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Pricing assumptions

General assumptions

The AWS Pricing Calculator is an estimation tool that provides an approximate cost of using AWS services based on the usage parameters that you specify. The AWS Pricing Calculator is not a quote tool, and does not guarantee the cost for your actual use of AWS services. The cost estimated by the AWS Pricing Calculator may vary from your actual costs for a number of reasons. Common reasons the estimate may be different from your actual cost include:

  1. Actual usage: Your actual cost will be based on your actual use of the services, not the Calculator. The accuracy of your inputs into the Calculator affects the accuracy of your actual costs. For example,
    1. If you estimate you will use a certain number of EC2 instances, but you actually use more, you will be billed for your actual utilization.
    2. If you use AWS services that you did not include in your estimate, then your estimate will differ from your actual bill.
    3. If you over or under estimate Data Transfer inputs or outputs for AWS services, your actual bill may vary.
    4. If you estimate your service use based on purchasing a 3-year reservation for a service, but you buy a 1-year reservation, your monthly and upfront prices will vary from the estimate.
  2. Region used: The prices for AWS services vary between Regions. Using different Region than the one used in the Calculator will affect the accuracy of the results.
  3. Change in prices: AWS offers pay-as-you-go pricing for most services and prices may change over time. If you buy services On Demand, your bill may be less or more than estimated, based on the current On Demand service rates. For certain services, you may buy a 1 or 3-year reservation to lock in the price as of the date of your reservation.
  4. Taxes: The Calculator does not include any taxes that may be applied to your purchase of the services.
  5. Time period: The Calculator assumes 730 hours in a month, (365 days in a year x 24 hours in a day / 12 months in year). The estimated, first twelve month’s total is calculated by 12 x total monthly cost + total upfront cost. The Calculator does not account for leap years, which adds one day.
  6. First 12-months total: The Calculator only shows your estimated totals up to the first 12 months. If you estimate costs with a 3 year, partial upfront pricing strategy, you will only see estimated costs adjusted for the first 12 months of the 3 year reservation.
  7. Free tier, promotional credits and discounts: The Calculator does not account for free tier pricing, promotional credits, or other discounts. You may be eligible for additional discounts that are not captured in the estimate. Contact Us for more information.
  8. Monthly billing period: AWS bills on a monthly basis. If your utilization starts mid-month, you will only see a portion of an actual month’s complete costs.
  9. Rounding: The Calculator performs mathematical rounding of pricing data. For details on how the Calculator rounds, refer to the pricing math contained in the “Show calculation” section of each service configuration.
  10. Tiered pricing: You may qualify for volume discounts based on your current use of AWS services, outside of what you estimate in the AWS Pricing Calculator. The Calculator does not account for usage that you do not include in the estimate. For example, if you already use 500 TB per month of Amazon S3 Standard storage, you pay $0.022 per GB. If you use the Calculator to estimate an additional 50 TB per month, the Calculator will assume this is the first 50 TB per month which is costed higher at $0.023 per GB. Your cumulative actual spend on 550 TB per month on Amazon S3 would be less than the estimated additional cost to your current spend.
  11. Per second billing: Some AWS services use per second billing. The Calculator does not account for per second billing options.
  12. Third-party licensing fees: The Calculator does not account for third-party licensing fees, such as software solutions deployed from AWS Marketplace.
  13. Currency: The Calculator estimates in U.S. dollars. Global exchange rates vary over time. If you translate your estimate to a different currency based on the current exchange, changes in the exchange rate will affect the estimate.

Amazon EC2 assumptions

  1. Burstable instances: Some instances have additional costs when it comes to burst capacity, (e.g., T2 and T3 unlimited instances). You accrue burst credits when running burstable instances, which you can use toward your bill, but if you exhaust those burst credits, you would need to pay additional costs for those overages. For more information on burstable instances, see Amazon EC2 instance types.
  2. Workloads: In order to deliver a cost-optimized pricing strategy, the Calculator performs a break-even analysis for your specified instance and workload. The analysis evaluates the cost for both on-demand and reserved instance scenarios and delivers a recommendation for either pricing model or a combination of the two for the most cost-effective solution.
    1. A workload is only as accurate as it is predictive of your actual workload. For example, if you use more than you estimate, you will be billed for more. If you use less, you will be billed for less.
    2. The break-even analysis is based upon a 730 hour month. Your actual month may have a different break-even point, and every instance has a different break-even point based on its own On Demand and Reserve Instance prices.
    3. Daily: There is an uneven distribution of days in a month. If you only run instances on Monday, we normalize how many Mondays are in a month. The actual may be 4 or 5 for the current month, but we average this to 4.3 Mondays in a month. (Example math: 730 hours in a month / (24 hours in a day * 7 days in a week) = 4.3452 occurrences of a specific day in a month.)
    4. Weekly: The Calculator assumes there are 4.34 weeks in a month.
    5. Monthly: The Calculator assumes there are 730 hours in a month.
    6. Custom: The Calculator assumes that all instances described in the custom workload are simultaneously running. When the Calculator performs a break-even analysis for a cost-optimized scenario, it does not know when the various custom workload instances are running, simultaneously or serially. If the instances are not running simultaneously, it may be cheaper to buy more reserved instances. To learn more, Contact Us.
  3. Spot pricing: With Spot instances, you pay the Spot price that's in effect for the time period your instances are running. The Spot pricing strategy assumes a historical average discount for the instance type you select but historical values may not be predictive of the actual discount at the time of your utilization. You may adjust the assumed discount as best fits your estimation model. However, the assumed discount is not a guarantee for your actual cost.
  4. Amazon Elastic Block Storage (EBS): For the Amazon Elastic Block Storage (EBS) estimate, the calculator assumes that your EBS snapshots are retained for one month, and then subsequently deleted.

AWS Budgets

If you are concerned about these potential variations, consider using AWS Budgets. AWS Budgets gives you the ability to set custom budgets that alert you when your costs or usage exceed (or are forecasted to exceed) your budgeted amount. You could also define actions you want to take in your account when a budget exceeds its threshold (actual or forecasted amounts). Learn more.