ERP Uptime SLA and Downtime Budget Calculator
An uptime target looks small until you convert it into minutes. 99.9% availability allows roughly nine hours of downtime in a year, and 99.99% allows under an hour. This calculator converts the target into a downtime budget and checks it against your planned maintenance and typical incident history.
Your numbers
8760 for 24x7 measurement. Use fewer hours if the SLA only counts business hours.
Patching, upgrades, restarts.
Lost output, idle labour, late shipment penalties. Estimate with finance.
Your results
Simple annual averages. Real SLAs differ in how they measure (monthly vs yearly, partial outages, excluded windows). Check your contract definitions before using the result in a negotiation.
Expected availability (%) vs time to restore
Sweeps Average time to restore from 0.5 to 12, holding your other inputs fixed.
Optional uptime review
Share your incident log summary and we will suggest where restore time or maintenance practice is consuming the budget.
Optional. The tool and every export work without this. No spam.
How to use it
Choose the uptime target in your SLA or the target you are considering. Enter the hours in the measurement year (8760 if the system must be up around the clock). Add planned maintenance per month and whether your SLA counts it. Then enter how many unplanned incidents you have per year and the average time to restore from your incident log. The calculator shows the allowed downtime, expected availability and how much budget remains.
- Use incident data from the last 12 months
- Read the contract definition of excluded maintenance
- Test several MTTR values with the chart
The formula
Allowed downtime equals measurement hours times one minus the target fraction. Expected availability is one minus counted downtime divided by measurement hours, shown as a percentage. Counted downtime is unplanned downtime (incidents multiplied by average restore time) plus planned maintenance if the SLA includes it. For comparison, a 24x7 year of 8760 hours gives about 87.6 hours at 99%, 43.8 at 99.5%, 8.8 at 99.9%, 4.4 at 99.95% and 0.9 at 99.99%.
Reading the result
A negative remaining budget means the target cannot be met with your current incident pattern. The most useful lever is often time to restore, not the number of incidents, which is why the chart sweeps it. Planned maintenance often becomes the main consumer of a tight budget, so many contracts exclude it or limit it to defined windows. The cost output reminds you why the target matters: a four hour weekly outage at a plant running ERP-driven scheduling can cost far more than the hosting fee.
Common mistakes
Common errors include comparing a 24x7 target to a business-hours measurement, ignoring partial outages such as slow performance or a failed integration, and assuming one nine of extra uptime costs a bit more when it usually costs several times as much. Another is accepting a vendor SLA that only credits money when you need availability. Finally, remember that your own ERP availability includes network, identity and database dependencies, not only the application server.
Frequently Asked Questions
How much downtime is 99.9% uptime?
About 8.8 hours per year on a 24x7 basis, roughly 43 minutes per month. It is a budget for all counted downtime together, not per incident.
Should planned maintenance count against the SLA?
It depends on the contract. Many SLAs exclude agreed maintenance windows, others count everything. For your internal ERP, counting it shows the real experience of users and plant staff, even if a vendor excludes it.
What uptime is realistic for an on-premise ERP?
It depends on redundancy, change discipline and staffing. Single-server setups with monthly patching often fall in the 99 to 99.5% range, while clustered designs with automated failover can aim higher. Measure your own history before promising a number.
Is this the same as an SLA credit calculator?
No. This planning tool shows the downtime budget and expected availability. A credit calculator works out the refund owed when a vendor misses its SLA, which is a separate question.
If you run your ERP on-premise and want clearer visibility of uptime and slow-query events, Netray can build monitoring and an operations assistant on top of your ERP logs. Contact us to scope it.
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