Cost Estimates, Worked Examples and Choosing a Host
Reserved instance vs on-demand: break-even worked example for an Indian business
Illustrative sums showing when a 1- or 3-year cloud commitment beats on-demand: break-even utilisation, upfront payment and early downsizing.
A one- or three-year cloud commitment pays off when a server would otherwise run more hours than the break-even utilisation, which equals the committed price divided by the on-demand price. With an illustrative 35% discount, break-even is 65% of the year: a server running 24×7 saves ₹42,000 a year on a ₹10,000-a-month on-demand bill, but one running only during office hours would lose money. This guide works through the sums, including upfront payment, early downsizing and dollar billing. It belongs to the best-fit method; the models themselves are explained in on-demand, reserved, savings plans and spot.
The break-even formula
- On-demand monthly price at 100% use: P
- Committed monthly price (paid whether used or not): C
- Break-even utilisation: C ÷ P
If the server would run more than that share of hours, commit; if less, stay on-demand and switch it off when idle.
Illustrative. P = ₹10,000, C = ₹6,500 (35% lower). Break-even = 6,500 ÷ 10,000 = 65% of hours, about 475 of 730 hours a month.
| Usage pattern | Hours a month | On-demand cost | Committed cost | Better choice |
|---|---|---|---|---|
| 24×7 production | 730 | ₹10,000 | ₹6,500 | Commit, save ₹3,500 |
| 18 hours a day | 548 | ₹7,507 | ₹6,500 | Commit, save ₹1,007 |
| Office hours, 12 h × 26 days | 312 | ₹4,274 | ₹6,500 | On-demand, save ₹2,226 |
| Batch job, 4 h a day | 120 | ₹1,644 | ₹6,500 | On-demand (or spot) |
On-demand cost = ₹10,000 × hours ÷ 730.
One year vs three years
| Option (illustrative) | Monthly equivalent | Yearly | Over 3 years |
|---|---|---|---|
| On-demand 24×7 | ₹10,000 | ₹1,20,000 | ₹3,60,000 |
| 1-year commitment, renewed twice | ₹6,500 | ₹78,000 | ₹2,34,000 |
| 3-year commitment | ₹4,500 | ₹54,000 | ₹1,62,000 |
The three-year option saves ₹72,000 more than renewing one-year terms, but only if the server is still needed at the same size in the same region for 36 months.
What happens if you downsize early
Suppose after 18 months you move the workload to a smaller server costing ₹5,000 on-demand, or to a managed database.
- 3-year commitment: you still pay ₹4,500 a month for the remaining 18 months (₹81,000) on top of the new server, unless the commitment can be exchanged, applied to other usage or resold under the provider's terms.
- 1-year commitments: the second term ends at month 24, so you pay ₹6,500 × 6 = ₹39,000 for the unused months.
Total 3-year cost with downsizing at month 18 (illustrative):
| First 18 months | Last 18 months | Total | |
|---|---|---|---|
| On-demand throughout | ₹1,80,000 | ₹90,000 (new ₹5,000 server) | ₹2,70,000 |
| 1-year commitments | ₹1,17,000 | ₹39,000 unused + ₹90,000 new | ₹2,46,000 |
| 3-year commitment | ₹81,000 | ₹81,000 unused + ₹90,000 new | ₹2,52,000 |
With the change of plan, the one-year option wins. A savings plan that applies across instance sizes or families could have absorbed part of the unused commitment; check what yours covers.
Upfront vs monthly payment
Paying all upfront usually earns a slightly deeper discount. Compare it with what that cash would earn or save elsewhere in the business.
Illustrative. A 1-year commitment costs ₹78,000 paid monthly or ₹74,000 all upfront. The upfront saving is ₹4,000, about 5.4% on money paid on average six months early, which is worth it only if your business does not need the cash for stock or payroll and has no cheaper use for it.
Dollar commitments
If the commitment is priced in dollars, an upfront payment fixes the rupee cost on the payment date. Monthly payments in dollars leave the rupee cost moving each month. A 4% move in the exchange rate can erase a large part of the gap between one-year and three-year discounts. See USD vs INR billing.
Step-by-step before you commit
- Measure each server's hours and size for two to three months, including a busy period.
- Commit only the steady baseline; leave peaks on-demand. See the festive-sale example.
- Rightsize first: committing to an oversized server locks in waste.
- Prefer flexible savings plans if your server mix may change.
- Start with one year; move to three only for stable systems.
- Diary the expiry date so that the price does not jump back to on-demand unnoticed.
Related guides
A scheduled office server is the classic case where a commitment does not pay; see the Windows accounting server example.
FAQ
Do commitments apply automatically?
Generally yes, to matching usage in the account or organisation, depending on the provider's rules. Check the coverage report after the first month.
Can I use the migration payback calculator for this?
The migration payback calculator measures a one-time cost against a yearly saving; an all-upfront commitment can be entered that way, but the break-even formula above is simpler.
What about GST on commitments?
GST applies when the supply is invoiced. For a foreign provider, reverse charge applies if you are registered. Ask your CA how to account for a prepayment.
Do VPS providers have commitments?
They usually offer discounts for prepaying months or years. The same break-even idea applies, plus refund terms.
Sources
- AWS EC2 pricing — on-demand and savings plan pages per region
- Google Cloud regions — regions where commitments apply
- CBIC GST — reverse charge on imported services
- Reserve Bank of India — reference exchange rates
