Understanding Azure Pricing: Pay-As-You-Go vs Reserved Instances

Microsoft Azure is now the cloud platform of choice for a large and growing number of UK businesses. From small companies running a single virtual machine to enterprises operating complex multi-tier applications, Azure provides the infrastructure, scalability, and global reach that modern businesses demand. Yet one aspect of Azure consistently causes confusion, frustration, and — when poorly managed — unnecessary expense: pricing.

Azure's pricing model is flexible, which is one of its strengths. But flexibility also means complexity. The same virtual machine can cost significantly different amounts depending on which pricing model you choose. Get it right, and you can save 40% to 72% compared to the default pricing. Get it wrong, and you could be paying thousands of pounds more than necessary every year.

This guide explains the two primary Azure pricing models — Pay-As-You-Go and Reserved Instances — in detail, compares them side by side, and helps you determine which approach is right for your business workloads.

How Azure Pricing Works: The Basics

Before comparing pricing models, it helps to understand how Azure charges for resources. Azure uses a consumption-based pricing model — you pay for the resources you use, measured in increments of time (typically per hour or per second) and quantity (such as gigabytes of storage or gigabytes of data transfer).

The cost of a virtual machine, for example, depends on several factors: the VM size (how many CPU cores and how much RAM), the operating system (Windows VMs cost more than Linux due to licensing), the Azure region (UK South and UK West have slightly different prices), the disk type and size, and the pricing model you choose.

It is this last factor — the pricing model — that offers the greatest opportunity for cost optimisation. Two identical virtual machines running the same workload 24 hours a day can have vastly different monthly costs depending on whether they are using Pay-As-You-Go or Reserved Instance pricing.

Pay-As-You-Go (PAYG) Pricing Explained

Pay-As-You-Go is Azure's default pricing model. As the name suggests, you pay for compute resources on a per-second or per-hour basis, with no upfront commitment. You can create a virtual machine, run it for three hours, delete it, and pay only for those three hours. There is no minimum term, no cancellation fee, and no obligation to continue using the resource.

Advantages of Pay-As-You-Go

PAYG pricing offers maximum flexibility. It is ideal for workloads that are temporary, unpredictable, or experimental. Development and testing environments, for example, often run only during business hours and can be shut down at weekends — PAYG pricing means you only pay for the hours they are actually running. Similarly, if you are piloting a new application and are unsure of the resource requirements, PAYG allows you to experiment without financial commitment.

Disadvantages of Pay-As-You-Go

The trade-off for flexibility is cost. PAYG pricing is the most expensive way to run workloads on Azure over the long term. If you have a virtual machine that runs 24/7/365 — such as a domain controller, a file server, or a line-of-business application server — the annual cost on PAYG pricing is significantly higher than the same machine on a Reserved Instance.

Reserved Instances (RIs) Explained

Reserved Instances represent a commitment to use a specific type and size of virtual machine for a one-year or three-year term. In exchange for this commitment, Azure provides a substantial discount compared to PAYG pricing — typically 30% to 40% for a one-year reservation and 55% to 72% for a three-year reservation.

The reservation is a billing construct, not a physical one. You are not reserving a specific physical server — you are committing to a certain level of usage, and Azure applies the discount to matching resources in your subscription. If you reserve a D4s v5 virtual machine in UK South for one year, any D4s v5 VM running in that region and subscription automatically receives the reserved pricing.

Advantages of Reserved Instances

The savings are substantial and predictable. For workloads that run continuously, the cost reduction is dramatic. A VM that costs £200 per month on PAYG might cost £120 per month with a one-year reservation or £80 per month with a three-year reservation. Over the life of the reservation, the savings can amount to thousands of pounds per machine.

Disadvantages of Reserved Instances

The commitment is binding. If your requirements change — you no longer need the VM, or you need a different size — you may not be able to use the reservation fully. Whilst Azure does allow you to exchange reservations for different VM sizes within the same family, you cannot cancel a reservation for a full refund. There is also the upfront planning required to identify which workloads are stable enough to warrant a reservation.

Cost Comparison: Real-World Examples

Let us examine the cost difference using a common Azure VM size used by UK SMEs. The D4s v5 is a popular general-purpose virtual machine with 4 vCPUs and 16 GB RAM, suitable for running applications such as line-of-business software, small databases, and file services.

Pricing Model	Monthly Cost (approx.)	Annual Cost (approx.)	3-Year Cost (approx.)	Saving vs PAYG
Pay-As-You-Go	£210	£2,520	£7,560	Baseline
1-Year Reserved	£135	£1,620	£4,860	36% saving
3-Year Reserved	£85	£1,020	£3,060	60% saving

For a single VM, the three-year reservation saves approximately £4,500 compared to PAYG over the same period. For a business running five or ten VMs, the savings multiply accordingly. This is not a marginal optimisation — it is a fundamental cost reduction that directly impacts your IT budget.

Azure Savings Plans: A Third Option

In addition to PAYG and Reserved Instances, Azure now offers Savings Plans — a newer pricing model that provides a discount in exchange for a commitment to a certain amount of hourly compute spending. Unlike Reserved Instances, which are tied to a specific VM size and region, Savings Plans apply across VM sizes, regions, and even compute services. This makes them more flexible than RIs, though the discount is typically slightly smaller.

Savings Plans are particularly useful for businesses with dynamic workloads that may change VM sizes or regions over the commitment period. They offer a middle ground between the flexibility of PAYG and the deep discounts of Reserved Instances.

Common Azure Cost Mistakes UK Businesses Make

Through our work with UK SMEs, we consistently see the same cost optimisation mistakes. Being aware of these can save your business significant sums.

Running everything on PAYG. Many businesses migrate to Azure and never review their pricing model. Every VM runs at the most expensive rate indefinitely, wasting thousands of pounds annually.

Leaving VMs running when not needed. Development and testing VMs that run 24/7, including weekends, when they are only used during business hours. Auto-shutdown schedules can reduce these costs by 70% or more.

Oversizing virtual machines. VMs provisioned with more CPU and RAM than the workload requires. Rightsizing — matching VM resources to actual usage — can reduce costs by 30% or more before any pricing model changes.

Ignoring Azure Advisor recommendations. Azure Advisor provides free, personalised recommendations for cost reduction, but many businesses never review them.

How Cloudswitched Optimises Azure Costs

At Cloudswitched, Azure cost optimisation is a core part of our managed cloud service. We conduct regular reviews of your Azure environment, identifying opportunities to reduce costs through rightsizing, Reserved Instance purchases, auto-shutdown policies, and resource cleanup. Our account managers present cost optimisation recommendations at every quarterly business review, ensuring your Azure spending stays aligned with your actual business needs.

We also manage the Reserved Instance purchasing process on your behalf, analysing your usage patterns to determine which workloads are suitable for reservations and which should remain on PAYG or Savings Plans. This blended approach ensures you benefit from the deepest possible discounts without sacrificing flexibility where it is needed.