Uptime / SLA Downtime Calculator
Uptime / SLA Downtime Calculator
Enter an uptime percentage — like the 99.9% or 99.99% figures commonly quoted in SLAs (Service Level Agreements) — to see exactly how much downtime that allows per day, month, and year.
The percentages compound faster than they might look at first glance: 99% ("two nines") still allows roughly 3.65 days of downtime per year, while 99.9% ("three nines") tightens that to about 8.77 hours, 99.99% ("four nines") to roughly 52.6 minutes, and 99.999% ("five nines") to just over 5 minutes annually. Seeing the actual time budget behind a percentage is far more useful than the percentage alone when negotiating an SLA or deciding what reliability target is realistic and worth the engineering investment to hit.
- Formula: Downtime = (1 − Uptime%) × Period Length, applied to a day, a 30.44-day average month, and a 365.25-day year.
- Common SLA tiers: 99% ("two nines") ≈ 3.65 days/year down; 99.9% ("three nines") ≈ 8.77 hours/year; 99.99% ("four nines") ≈ 52.6 minutes/year; 99.999% ("five nines") ≈ 5.26 minutes/year.
- Why this matters: a seemingly tiny difference like 99.9% vs. 99.99% represents a roughly 10x difference in allowed downtime — useful context when comparing vendor SLA guarantees.
What uptime is "good enough" for my service?
It depends on the cost of downtime — a critical payment system might need 99.99%+, while an internal reporting dashboard might be fine at 99% or even lower.
Does an SLA guarantee I'll never see more downtime than this?
No — an SLA is a contractual target with often financial penalties (service credits) if missed, not a technical guarantee; actual downtime can exceed the SLA figure.
Uptime / SLA Downtime Calculator
Enter an uptime percentage — like the 99.9% or 99.99% figures commonly quoted in SLAs (Service Level Agreements) — to see exactly how much downtime that allows per day, month, and year.
The percentages compound faster than they might look at first glance: 99% ("two nines") still allows roughly 3.65 days of downtime per year, while 99.9% ("three nines") tightens that to about 8.77 hours, 99.99% ("four nines") to roughly 52.6 minutes, and 99.999% ("five nines") to just over 5 minutes annually. Seeing the actual time budget behind a percentage is far more useful than the percentage alone when negotiating an SLA or deciding what reliability target is realistic and worth the engineering investment to hit.
- Formula: Downtime = (1 − Uptime%) × Period Length, applied to a day, a 30.44-day average month, and a 365.25-day year.
- Common SLA tiers: 99% ("two nines") ≈ 3.65 days/year down; 99.9% ("three nines") ≈ 8.77 hours/year; 99.99% ("four nines") ≈ 52.6 minutes/year; 99.999% ("five nines") ≈ 5.26 minutes/year.
- Why this matters: a seemingly tiny difference like 99.9% vs. 99.99% represents a roughly 10x difference in allowed downtime — useful context when comparing vendor SLA guarantees.
What uptime is "good enough" for my service?
It depends on the cost of downtime — a critical payment system might need 99.99%+, while an internal reporting dashboard might be fine at 99% or even lower.
Does an SLA guarantee I'll never see more downtime than this?
No — an SLA is a contractual target with often financial penalties (service credits) if missed, not a technical guarantee; actual downtime can exceed the SLA figure.