To calculate customer usage for billing, define the billable unit, connect each valid usage event to the right customer and billing period, aggregate it using the contract’s rules, then apply the agreed price schedule. A useful starting point is bill = base charge + usage charge − applicable credits. For a simple per-unit rate, usage charge equals billable units multiplied by the unit price; packages, tiers, allowances and credits require their own contract rules.
1. Define what counts as billable usage
Choose an activity and a unit the customer can understand, such as requests, data volume, compute time, instances, or hosts scanned. Azure describes a billing increment as an amount of usage that incurs a cost and gives time, instances, data size and requests as examples. AWS Marketplace guidance likewise gives examples such as data received or retained, requests, compute time and distinct hosts scanned.
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Make the definition precise: state which activity qualifies, how the quantity is measured, and what unit appears on the invoice. Internal telemetry is not automatically billable; it should correspond to a clearly disclosed customer-facing measure. Neither Azure nor AWS prescribes one best unit for every service.
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2. Record usage against the customer and time
Capture enough information to determine who generated the usage, when it occurred and how much qualifies. A practical usage record includes:
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- A stable customer, tenant or subscription identifier.
- The event timestamp and billable quantity.
- The usage dimension or event type, such as requests or data received.
- A unique event identifier where applicable, to help detect duplicate submissions.
An AWS Partner Network integration example describes billing events with tenant, event time and quantity before aggregation. For implementation details, see AWS Partner Network’s SaaS integration example. The exact retry and duplicate-handling policy depends on the product, but the system should be designed to avoid charging twice for the same event.
3. Validate events before aggregating
Before calculating a period total, check that each event belongs to a customer with an applicable entitlement and falls within the correct billing period. Investigate missing identifiers, invalid quantities and events outside an active subscription rather than silently including them.
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Keep enough event-level detail to explain how a total was produced and to investigate a customer dispute. This is especially important if the billing platform does not allow a submitted usage record to be changed later.
4. Aggregate usage using the meter’s rule
For an additive meter, sum eligible quantities for each customer, usage dimension and billing period. But do not assume every measure is a simple sum: a contract might charge for peak usage, the last observed value, a count of unique items, or another non-additive measure. Apply the rule that defines the meter.
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For example, if a contract charges per request, the period quantity may be the total eligible requests. If it charges for peak concurrent instances, summing every instance observation would not calculate the same measure. The billing rule must match the unit and pricing terms the customer agreed to.
5. Apply the contract’s pricing model
Once the billable quantity is established, apply the relevant base fee, included allowance, rate, package, threshold, tier or credits. Stripe identifies several usage-based pricing approaches; their mechanics are not interchangeable.
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| Pricing approach | How to calculate the usage charge | Contract details to verify |
|---|---|---|
| Per unit or pay as you go | Eligible units × applicable unit rate | Rate, unit definition and any rounding rule |
| Fixed fee plus overage | Base fee, plus the charge for eligible usage above the included allowance | Allowance, overage rate and threshold treatment |
| Package or bundle | Apply the package price and the rules for the quantity purchased or consumed | Package size and treatment of unused usage |
| Credit burndown | Deduct the value of eligible usage from the available prepaid or committed credits | Credit value, consumption rules and any expiration or rollover terms |
Stripe describes these models at Usage-based billing: What it is and how it works. Specific refund, expiration and rollover terms must come from the applicable contract. Taxes, proration, minimums and rounding can also depend on the provider and signed price schedule, so do not assume a universal calculation.
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Choose how often usage is reported based on customer visibility, operational cost and the rules of the billing platform. Platform-specific instructions differ:
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- AWS Marketplace SaaS metering: AWS recommends hourly reporting. It warns that longer intervals reduce granularity and can create reporting risks around cancellation or delayed submission. In this workflow, a dimension’s usage record cannot be amended after it is reported, so validate it first and retain an internal audit trail. See AWS Marketplace metering for usage.
- Microsoft Marketplace: guidance says to accumulate multiple units consumed within an hour into one usage event. See Microsoft Marketplace metering service APIs.
These are marketplace-specific instructions, not universal rules for every billing provider or contract.
7. Make the invoice reconcilable
Show enough information for the customer to compare the invoice with its own records. A useful breakdown identifies the usage quantity, unit, billing period, applicable rate or pricing rule, included usage or credits, and resulting charge. AWS Marketplace can display product dimensions as separate line items, but that visibility is specific to its marketplace.
AWS Marketplace documentation explains: “AWS calculates a customer’s bill using the metering data along with the prices that you provided when you created your product.” That captures the central calculation: metered usage is only one input; the configured or contracted pricing determines the bill.
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