Azure Reservations, Spot Instances, and Pay-As-You-Go Pricing Explained

Azure gives you three fundamentally different ways to pay for compute: Pay-As-You-Go charges the standard rate with no commitment, Reservations trade a one- or three-year commitment for a meaningfully discounted rate, and Spot Virtual Machines offer the deepest discount of all in exchange for accepting that the workload can be interrupted at any time. Picking correctly among the three — and knowing when Azure Hybrid Benefit adds a further discount on top — is one of the most scenario-heavy topics on the AZ-900 exam.

Three ways to pay for Azure compute

	Pay-As-You-Go	Reservations	Spot Virtual Machines
Commitment required	None	1- or 3-year term	None
Relative price	Standard published rate	Discounted vs. Pay-As-You-Go	Deepest discount, variable
Availability guarantee	Guaranteed while running	Guaranteed while running	Can be evicted with little notice
Best fit	Short-term, unpredictable, or new workloads	Steady, continuous, predictable workloads	Interruptible, checkpoint-able, flexible-schedule workloads
Payment structure	Billed as consumed	Paid upfront or in monthly installments	Billed as consumed, at spot rates

Pay-As-You-Go: maximum flexibility, standard price

Pay-As-You-Go is the default. You’re charged the published rate for exactly what you consume, with no term commitment and no penalty for stopping at any time. It’s the purest expression of the OpEx model covered in CapEx vs OpEx cloud economics — it’s the right choice for workloads whose usage pattern isn’t known yet, a new project, a proof of concept, or anything whose long-term shape hasn’t stabilized. The tradeoff is that you’re leaving money on the table for any workload that turns out to run continuously and predictably, since that’s precisely the usage pattern Reservations are priced to reward.

Reservations: locking in a rate for predictable usage

An Azure Reservation is a commitment to use a given amount of a resource — commonly virtual machine capacity, but reservations exist across many Azure service categories, not just compute — for a fixed one- or three-year term, in exchange for a substantially lower rate than Pay-As-You-Go. You can pay for the reservation as a single upfront amount or spread the cost across monthly installments; either way, the discounted rate is locked in for the full term regardless of how the published Pay-As-You-Go price moves in the meantime. Reservations bill for the reserved capacity whether or not the workload is actually running, so the savings come from the discounted rate itself, not from powering things off — a subtlety AZ-900 likes to test directly. The fit is a workload with steady, continuous, well-understood capacity needs stretching a year or more into the future: a production database, a core line-of-business application, anything that’s effectively always on.

Spot Virtual Machines: the cheapest price, with strings attached

Azure Spot Virtual Machines let you buy unused Azure compute capacity at a steep discount compared to Pay-As-You-Go, with the catch that Azure can evict the virtual machine with little warning whenever it needs that capacity back for a full-price customer. There’s no term commitment involved at all — you can walk away anytime, and Azure can reclaim the capacity anytime. This makes Spot VMs a strong match for workloads that can tolerate interruption and resume from where they left off: batch rendering jobs, large-scale data processing that checkpoints its progress, or any task with no fixed deadline. It’s a poor match for anything requiring guaranteed uptime, like a production database or a customer-facing web front end — evicting either mid-request is exactly the failure mode those workloads can’t absorb.

Azure Hybrid Benefit: a licensing lever, not a usage discount

Azure Hybrid Benefit is easy to confuse with a purchasing option, but it’s really a licensing benefit. If your organization already owns on-premises Windows Server or SQL Server licenses covered by Software Assurance, Azure Hybrid Benefit lets you apply those existing licenses toward the cost of running equivalent virtual machines in Azure, so you’re not paying for that license a second time inside the VM rate. It has nothing to do with how long a VM has run, and it isn’t a free allotment of hours — it depends entirely on holding eligible licenses already, and it can stack with a Reservation for compounding savings.

Matching pricing options to real workload patterns

Picking the wrong pricing option is just one lever behind a surprising bill — see what affects your Azure bill for the fuller list of cost factors beyond the purchasing option alone. The exam frequently presents an organization running two or three workloads at once and asks which combination of pricing options minimizes cost without breaking each workload’s requirements. The pattern to internalize: reserve what’s steady and always-on, spot-price what’s interruptible and flexible, and leave Pay-As-You-Go for anything unpredictable or short-lived. A mission-critical database that must run continuously for three years gets a Reservation. A nightly batch job that tolerates being paused gets Spot pricing at the deepest discount. A customer-facing app with spiky, hard-to-predict traffic stays on Pay-As-You-Go so you’re never paying for capacity you didn’t end up using. Putting every workload on the same pricing option — all Reserved, or all Spot, or all Pay-As-You-Go — is almost always the wrong answer, because it either wastes committed spend on capacity that isn’t always running or risks eviction on something that can’t tolerate it.

Predictability as a distinct cloud benefit

AZ-900 also frames Reservations as a way to achieve “predictability” — a named cloud benefit separate from the pricing option itself. Predictability covers both cost (knowing what you’ll be billed) and performance (knowing what response time or behavior to expect), and a Reservation supports the cost half by locking in a fixed rate for its term. Pairing a Reservation with proactive budgets and spend alerts — the kind of tooling covered in Azure Cost Management, budgets, and tags — is the combination the exam treats as the full answer to “how do we keep cloud costs predictable,” since a locked-in rate plus active monitoring covers both the pricing side and the oversight side. For the deeper mechanics of applying Reservations, Hybrid Benefit, and Spot VMs to cut a live compute bill, see Azure Reservations, Hybrid Benefit, and Spot VMs.

How the AZ-900 exam tests this

• A scenario describes steady, continuous, multi-year usage and asks which purchasing option reduces cost versus Pay-As-You-Go. The answer is a Reservation; distractors involve switching deployment models or simply buying more VMs, neither of which lowers cost.
• A scenario describes a workload that can be paused or interrupted and wants the lowest possible price, with no willingness to commit to a term. The answer is Spot Virtual Machines; a Reservation is the trap because it requires exactly the commitment the scenario rules out.
• A multi-workload scenario asks for the single combination of pricing options that minimizes total cost across a steady database, an interruptible batch job, and an unpredictable web app. The correct combination is Reservation, Spot, and Pay-As-You-Go respectively — uniform answers (all Reserved, all Spot) are always wrong.
• A question describes an organization applying existing on-premises Windows Server or SQL Server licenses to Azure VM costs. That’s Azure Hybrid Benefit specifically, not a Reservation and not a Spot discount — the licensing detail is the giveaway.
• A predictability-themed stem asks which benefit lets an organization forecast spend based on pricing tools and usage patterns. The answer is cost predictability, distinct from elastic scaling, fault tolerance, or governance, even when a Reservation is the mechanism mentioned in the same sentence.

Quick reference

• Pay-As-You-Go: no commitment, standard rate, best for unpredictable or new workloads.
• Reservations: 1- or 3-year commitment, discounted fixed rate, best for steady, always-on usage; billed whether or not the resource runs.
• Spot Virtual Machines: no commitment, deepest discount, can be evicted; best for interruptible, checkpoint-able work.
• Azure Hybrid Benefit: applies existing licensed Windows Server/SQL Server rights (with Software Assurance) to Azure VM costs — a licensing discount, not a usage discount.
• Multi-workload questions want you to match each workload to the option that fits its interruption tolerance and duration, not apply one option to everything.
• Reservations support the “predictability” cloud benefit by locking a rate in advance; pairing them with cost monitoring covers both cost and oversight.
• Once the three-way comparison is second nature, practice AZ-900 questions that combine pricing options across multiple workloads in a single scenario.