SLA Uptime Calculator
Allowed Downtime (99.9% SLA)
Break-Even Analysis
Moving to 99.95% costs $3000/mo extra but only saves $50/mo in avoided downtime
The next nine is NOT worth the investment at current revenue.
All SLA Tiers
| SLA↕ | Downtime / Year↕ | Downtime / Month↕ | Infra Cost/mo↕ | Loss / Hour↕ |
|---|---|---|---|---|
| 99% | 3d 15h 40m | 7h 18m | $500.00 | $136.99 |
| 99.9% | 8h 46m | 43.8m | $2,000.00 | $136.99 |
| 99.95% | 4h 23m | 21.9m | $5,000.00 | $136.99 |
| 99.99% | 52.6m | 4.4m | $15,000.00 | $136.99 |
| 99.99900000000001% | 5.3m | 26.3s | $50,000.00 | $136.99 |
An SLA target like "three nines" sounds precise until you translate it into real downtime: 99.9% uptime allows nearly nine hours of outage a year, while 99.999% allows just over five minutes. This calculator converts any SLA target from 99% to 99.999% into allowed downtime per year, quarter, month, week, and day, estimates the revenue lost per hour of outage, and runs a break-even analysis on whether chasing the next nine is worth the added infrastructure cost.
Formula
Downtime = (1 − uptime) × period minutes; Revenue loss/hr = monthly revenue ÷ 730
- uptime
- SLA target as a fraction (0.999 for 99.9%)
- period minutes
- Minutes in the window: 525,960/year, 43,830/month, 10,080/week, 1,440/day
- 730
- Approximate hours per month (365.25 × 24 ÷ 12)
- error budget
- (1 − uptime) × 43,830 — the allowed downtime minutes per month
How it works
- Choose your SLA target (99%, 99.9%, 99.95%, 99.99%, or 99.999%) and enter your monthly revenue so the tool can price an hour of downtime.
- It converts the uptime percentage into allowed downtime across time windows and the monthly error budget in minutes, using 525,960 minutes per year and 43,830 minutes per month.
- It then compares your tier against the next nine: the extra infrastructure cost versus the revenue protected by the reduced downtime, and reports whether the upgrade pays for itself.
Worked example
A service targeting 99.9% uptime with $1,000,000 in monthly revenue, comparing whether to move to 99.95%.
- Allowed downtime/year = (1 − 0.999) × 525,960 ≈ 526 min ≈ 8h 46m; monthly error budget ≈ 43.8 min.
- Revenue loss per hour = 1,000,000 ÷ 730 ≈ $1,370.
- Moving 99.9% → 99.95% cuts monthly downtime from ~43.8 to ~21.9 min, saving ~0.365 h × $1,370 ≈ $500/mo in avoided loss.
- Default infra cost rises from $2,000 to $5,000/mo, a $3,000 increase.
99.9% allows about 8h 46m of downtime per year (43.8 min/month). The jump to 99.95% saves only ~$500/mo in avoided loss but adds $3,000/mo in infrastructure, so it does not pay off at this revenue level.
Frequently asked questions
- How much downtime does each SLA tier allow?
- Per year, 99% allows about 3.65 days, 99.9% about 8h 46m, 99.95% about 4h 23m, 99.99% about 53 minutes, and 99.999% about 5 minutes 16 seconds. Each additional nine cuts the allowed downtime by roughly a factor of ten.
- What is an error budget?
- The error budget is the allowed downtime over a period — the inverse of your SLA. At 99.9% you have roughly 43.8 minutes of budget per month. Teams spend that budget on risk (deploys, experiments) and slow down releases when it runs low.
- How is revenue loss per hour calculated?
- It divides monthly revenue by about 730 hours per month, assuming revenue accrues evenly. This is a simplification; real impact depends on time-of-day traffic, whether the outage is total or partial, and reputational effects beyond direct lost sales.
- Is more uptime always worth it?
- Not necessarily. Each added nine often multiplies infrastructure and operational cost while protecting steadily less revenue. The break-even analysis here compares the marginal infrastructure cost against the revenue saved by reduced downtime so you can decide if the next nine is justified.