--- title: SLA Calculator – Allowed Downtime per Tier description: Free SLA calculator. See how much downtime an SLA of 99%, 99.9%, 99.95% or 99.99% actually permits per day, week, month and year, convert an outage back into a percentage, and estimate what the downtime costs at your revenue. Instant, no signup. canonical: https://watchfor.io/sla-calculator --- [Back to all free tools](/free-tools) # SLA Calculator Translate an SLA into numbers you can hold a vendor to — how much downtime 99.9%, 99.95% or 99.99% actually permits per day, week, month and year, in both directions, and what that downtime costs at your revenue. Compare tiers before you sign, or check whether last month's outage breached the agreement. Free, instant, no signup. An SLA is written as a percentage and lived as minutes. "99.9% monthly availability" sounds close to perfect and permits 43 minutes of downtime every month; 99.99% permits four. Vendors know this, and so should the person signing — or the person on call who has to decide whether a 20-minute outage has already used the month's allowance. Enter the SLA percentage and the calculator shows the allowed downtime for every period, or enter the outage you had and get the availability it produced. Add your hourly revenue and the same numbers turn into what a breach of each tier costs, which is usually the number that decides how much to spend on redundancy. Uptime percentage SLA level % Display Downtime Uptime Revenue (optional) $ Daily Downtime 1m 26s Weekly Downtime 10m 5s Monthly Downtime 43m 12s Yearly Downtime 8h 45m 36s ### Downtime cost estimation $ 100 Hour Day Month Year ## How to use the Uptime Calculator Using our calculator is simple and provides instant insights into your service availability: - Enter your uptime percentage – Most services aim for 99% uptime or higher. Enter the percentage you want to analyze to see how it translates to actual downtime. - Choose between uptime or downtime display – Toggle between viewing the time your service is operational versus when it's unavailable. - Add revenue (optional) – Input your business revenue to calculate the financial impact of downtime. Select your revenue interval (hourly, daily, monthly, or yearly) for accurate cost estimation. - Get instant results – The calculator automatically shows you downtime across different time periods (daily, weekly, monthly, and yearly) and estimates potential revenue loss. For example, if your service has 99.9% uptime, that means 8 hours and 45 minutes of downtime per year. Want to know the impact of increasing your uptime to 99.99%? Simply adjust the input and see the difference instantly. ## What is uptime? Uptime refers to the percentage of time a system, server, or website remains operational and accessible. It's a key performance indicator for reliability and is typically measured as a percentage. For instance: - 99% uptime means the service is available for 361 days per year, with about 3.65 days of downtime. - 99.9% uptime means about 8.76 hours of downtime per year. - 99.99% uptime reduces downtime to about 52 minutes per year. - 99.999% uptime limits downtime to approximately 5.26 minutes per year. A higher uptime percentage means fewer interruptions, which is crucial for businesses that depend on continuous service availability. Uptime is often included in Service Level Agreements (SLAs) to guarantee a minimum level of availability to customers — our guide to [what 99.9% uptime really means](/blog/what-is-99-9-percent-uptime) walks through the maths in depth, and [how to read an SLA report](/blog/honest-sla-reports) covers where published numbers bend the truth. ## What is an optimal amount of uptime? The ideal uptime percentage depends on the needs of your business and your customers' expectations. While 100% uptime is unrealistic due to maintenance windows, hardware failures, and unexpected issues, the goal is to minimize downtime to a level where it does not significantly disrupt operations or impact users. For most businesses, the following uptime percentages serve as benchmarks: - 99.9% uptime ("three nines") – Suitable for general web hosting, SaaS platforms, and e-commerce businesses where occasional downtime is acceptable. This translates to about 8.77 hours of downtime per year. - 99.95% uptime – A middle ground offering about 4.38 hours of downtime per year, appropriate for businesses that need higher reliability without the cost of enterprise-grade infrastructure. - 99.99% uptime ("four nines") – A better target for financial institutions, healthcare systems, and critical online services that require higher reliability. This allows only 52.6 minutes of downtime per year. - 99.999% uptime ("five nines") – The gold standard for mission-critical applications like telecom services, payment processors, and data centers, where even seconds of downtime can have major consequences. This permits only 5.26 minutes of downtime annually. An optimal uptime level is one that balances cost and performance while ensuring an uninterrupted experience for users. If downtime leads to lost revenue, customer churn, or safety risks, a higher uptime target is necessary. Remember that achieving higher uptime typically requires more investment in redundancy, monitoring, and infrastructure. ## How do you calculate downtime & uptime? Calculating uptime and downtime is straightforward with the right formula. Here's how it works: Uptime Percentage = (Total Time - Downtime) / Total Time × 100 Downtime = Total Time × (1 - Uptime Percentage / 100) For example, if you want to calculate downtime for 99.9% uptime over a year: - Total time in a year: 365 days × 24 hours = 8,760 hours - Downtime allowed: 8,760 × (1 - 99.9 / 100) = 8,760 × 0.001 = 8.76 hours Our calculator automates this process, breaking down the results into daily, weekly, monthly, and yearly time periods. It also factors in your revenue to estimate the financial impact of downtime, helping you understand the true cost of service interruptions. ## How to prevent downtime? Preventing downtime requires a proactive approach to infrastructure management, monitoring, and incident response. Here are key strategies to minimize service interruptions: - Implement robust monitoring – Use uptime monitoring tools to detect issues before they impact users. Monitor your websites, APIs, servers, and critical services 24/7 from multiple locations. - Set up redundancy – Deploy multiple servers, load balancers, and failover systems to ensure service continuity if one component fails. Use geographically distributed infrastructure for disaster recovery. - Perform regular maintenance – Schedule updates, patches, and maintenance during off-peak hours. Test changes in staging environments before deploying to production. - Automate backups – Implement automated backup solutions and regularly test restoration procedures. Keep backups in multiple locations for added protection. - Use a CDN – Content Delivery Networks improve availability by distributing content across global servers, reducing the load on your primary infrastructure. - Plan for scaling – Ensure your infrastructure can handle traffic spikes. Use auto-scaling solutions to adjust resources based on demand. - Have an incident response plan – Document procedures for common issues and maintain an on-call rotation. Quick response times minimize the impact of outages. - Monitor dependencies – Track the health of third-party services, APIs, and external dependencies that your application relies on. The most effective way to prevent costly downtime is to combine comprehensive monitoring with proactive maintenance and robust infrastructure. WatchFor's [uptime monitoring](/http-monitoring) checks your sites and APIs from multiple regions and confirms a failure before alerting, and a [status page](/status-pages) keeps customers informed while you fix it. ## Common SLA uptime levels Service Level Agreements (SLAs) define the expected uptime for a service. Here's a quick reference table showing how different uptime percentages translate to actual downtime: Uptime % Downtime per day Downtime per month Downtime per year 99% 14.4 minutes 7.2 hours 3.65 days 99.5% 7.2 minutes 3.6 hours 1.83 days 99.9% 1.44 minutes 43.2 minutes 8.77 hours 99.95% 43.2 seconds 21.6 minutes 4.38 hours 99.99% 8.64 seconds 4.32 minutes 52.6 minutes 99.999% 0.86 seconds 25.9 seconds 5.26 minutes Understanding these benchmarks helps you set realistic uptime targets and communicate expectations with customers. Use the calculator above to model your specific uptime requirements and their financial impact — and once you've picked a target, the only way to know you're hitting it is to [measure it continuously](/monitoring). ## Frequently asked questions How much downtime does 99.9% allow? 8 hours 46 minutes a year, 43 minutes 50 seconds a month, 10 minutes 5 seconds a week, 1 minute 26 seconds a day. Each extra nine divides those by ten: 99.99% is 52 minutes a year and 4 minutes 23 seconds a month. What is the difference between SLA, SLO and SLI? The SLI is the measurement (successful requests ÷ total requests). The SLO is the internal target you aim for (99.95%). The SLA is the external promise with consequences attached (99.9%, or service credits). Teams set the SLO tighter than the SLA so they notice trouble before the contract does. Monthly or annual — which period does an SLA use? Read the contract; most cloud SLAs are per calendar month, so a bad month can't be averaged away by eleven good ones. The calculator shows every period because vendors quote annual figures when they sound better and monthly ones when they're enforced. Does scheduled maintenance count against the SLA? Usually not, if it was announced within the notice period the contract defines — which is why SLAs specify a maintenance window. Unplanned downtime always counts. Check whether the SLA measures the whole service or only the parts the vendor controls. What do SLA credits typically look like? A percentage of the monthly bill, tiered by how far availability fell: for example 10% below 99.9%, 25% below 99%, 100% below 95%. Credits are almost always capped at the month's fee, so the calculator's cost estimate — your revenue lost — is the number the credit does not cover. How do I know whether a vendor met its SLA? Measure it yourself, from outside, continuously. A vendor's own status page is measured by the vendor. Independent uptime monitoring with incident timestamps gives you the record to claim a credit with — WatchFor's reports produce exactly that per month. ## Know your real uptime — not the estimate This calculator shows what a percentage costs. Monitoring shows what you actually get: checks from multiple regions, confirmed incidents, and alerts via email, Slack, Telegram, PagerDuty and more. 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