AWS Savings Plans vs Reserved Instances for EC2 — Sydney t4g / t3a

TL;DR

• All four plans cover t4g. If you stay on t4g, the EC2 Instance Savings Plan (t4g, Sydney) is cheapest: 37% off for 1 yr, 57% off for 3 yr, No Upfront.
• Compute SP costs the same as a Convertible RI (22% / 44% off) and follows you to t3a by itself. A Convertible RI only does that through manual exchanges, so skip it.
• On day 1 a Compute SP fixes a $/hour amount, the term and the payment option. It fixes no instance. Commit what runs 24/7 today: one t4g.micro = $0.0083/h (1 yr).
• A Standard RI can only change size inside t4g. A Convertible RI can switch to t3a, but only to equal-or-higher value, in the same region, with the same end date.
• Verdict: if moving to t3a is a real option, buy a Compute SP, 1 yr, No Upfront. If you'll stay on Graviton, buy an EC2 Instance SP for t4g, 3 yr.

Scenario: EC2 only, Linux, shared tenancy, always Sydney (ap-southeast-2), running 24/7. No Lambda or Fargate. Today it's one t4g.micro, and it may move to t4g.medium or t3a. Prices: USD, from the AWS Price List API (EC2 offer file and Savings Plans file 20261003071546), pulled 2026-10-05. A month is 730 h.

The four options in one line each

Option	What you commit to	Where it applies	Best for — choose it when
Compute Savings Plan	$X per hour of spend, at Savings Plan rates	Any EC2 family, size, OS, tenancy or region, plus Fargate and Lambda	You might move to t3a/x86 before roughly 85% of the term, change region, or add Lambda/Fargate
EC2 Instance Savings Plan	$X per hour of spend, at Savings Plan rates	One family in one region (e.g. t4g in Sydney), any size, OS or tenancy	You'll stay on t4g in Sydney for the whole term. The default pick
Convertible RI	N instances of one type	That type, in one region. You can change it by exchanging the RI by hand.	Rarely. A Compute SP gives the same 22% / 44% off without manual exchanges
Standard RI	N instances of one type	That type, in one region. Size can flex within the family. Family can never change.	You need a zonal capacity reservation, or the option to sell it on the RI Marketplace (needs a US bank)

The * on "Convertible RIs*" in AWS's comparison table means the same thing: "Convertible RIs can be changed across instance family, instance size, OS, and tenancy, but requires you to manually perform exchanges."

Price pairs: there are really only two discount levels

In the Sydney price files, each Savings Plan has the same rate as one RI type, to within rounding:

Discount level	Products	t-family, 1 yr	t-family, 3 yr
Flexible	Compute SP = Convertible RI	22% (No Upfront) – 27% (All Upfront)	44% – 50%
Locked to one family	EC2 Instance SP = Standard RI	37% – 41%	57% – 62%

AWS advertises "up to 66%" and "up to 72%". t4g and t3a in Sydney reach about 50% and 62%.

Which plan should I buy? Answer five questions

Go down the questions in order. An answer can rule plans out, and the table says why. Then buy the cheapest plan still standing, in this order:

1. EC2 Instance SP: 37% / 57% off
2. Standard RI: same price, more rules
3. Compute SP: 22% / 44% off
4. Convertible RI: same price as Compute SP, plus manual exchanges

The questions

#	Question	If you answer…	✅ Still OK	❌ Ruled out, and why
1	Will it run 24/7 for the whole term (at least 1 yr)?	No	On-Demand only	All four. You pay for every hour of the term, running or not. A 1 yr plan only pays off if the instance runs more than ~78% of hours (Compute SP, Convertible RI) or ~63% (EC2 Instance SP, Standard RI).
2	Might it leave Sydney, or might you add Fargate or Lambda?	Yes	Compute SP	EC2 Instance SP, Standard RI, Convertible RI. All three are fixed to Sydney and to EC2 for the whole term.
3	Might it move off t4g (e.g. to t3a for x86) before the last ~15% of the term?	Yes, or not sure	Compute SP, Convertible RI	EC2 Instance SP, Standard RI. The family is fixed. After the move the commitment is wasted every hour and the new instance is billed On-Demand.
4	Do you need capacity guaranteed in one Availability Zone?	Yes	Standard RI (zonal), Convertible RI (zonal)	Both Savings Plans. They only discount the price. They never reserve capacity.
5	Do you need a way out before the term ends?	Yes, and you have a bank with a US address	Standard RI	EC2 Instance SP, Compute SP: they can only be returned in the first 7 days. Convertible RI: it can't be sold.
		Yes, but no US bank	none of them	No plan has an exit for you. Buy 1 yr, not 3 yr, and commit only to what runs today.

If every plan is ruled out, two answers conflict. For example, "yes" to Q2 (might leave Sydney) and "yes" to Q4 (need zonal capacity) leave nothing. Decide which need matters more, or stay On-Demand.

Then pick the term, payment and amount

Question	Answer → choose
Are you sure of it for 3 years? (same family for an EC2 Instance SP or RI, same spend for a Compute SP)	Yes → 3 yr: 57% instead of 37% off on an EC2 Instance SP, 44% instead of 22% on a Compute SP. No → 1 yr.
Can you pay up front?	Yes → All Upfront, about 4–5 more points off. No → No Upfront. Partial Upfront sits in between.
How much do I commit? (Savings Plans)	What runs 24/7 today, at the Savings Plan rate. For one t4g.micro, 1 yr No Upfront: $0.0067/h on an EC2 Instance SP, $0.0083/h on a Compute SP. See Q3.

Your result: what to buy, and why not the others

A. "Yes" to Q1, "no" to Q2–Q5: staying on t4g in Sydney

• ✅ EC2 Instance Savings Plan, t4g, Sydney. 37% / 57% off, and it covers any t4g size without you doing anything.
• ❌ Standard RI: the same price, but it is tied to one instance size. A t4g.micro RI covers only a quarter of a t4g.medium, and you change it by hand.
• ❌ Compute SP: 15 points less discount (22% vs 37%) for flexibility you said you don't need.
• ❌ Convertible RI: the same low discount as a Compute SP, plus manual exchanges.

B. "Yes" to Q3: might move to t3a

• ✅ Compute Savings Plan, 1 yr, No Upfront. It follows the instance to t3a by itself and still covers about 89% of a t3a.micro.
• ❌ EC2 Instance SP, Standard RI: locked to t4g. Moving at month 6 costs $110.81 for the year, against $78.31 on a Compute SP (see the break-even table).
• ❌ Convertible RI: the same discount as a Compute SP, but each move is a manual exchange. The new value can only stay the same or go up, the end date doesn't change, and it can't be sold.

C. "Yes" to Q2: might leave Sydney, or add Fargate / Lambda

• ✅ Compute Savings Plan. It is the only one of the four that works in any region and also covers Fargate and Lambda.
• ❌ EC2 Instance SP, Standard RI, Convertible RI: all three stay in Sydney and only cover EC2. After a move to another region they cover nothing.

D. "Yes" to Q4: need guaranteed capacity in one AZ

• ✅ Standard RI, zonal. If Q3 was also "yes", a zonal Convertible RI instead.
• ❌ EC2 Instance SP, Compute SP: they discount the price but never reserve capacity.
• ⚠️ A zonal RI loses size flexibility. It covers only that exact size in that AZ.

E. "Yes" to Q5, with a US bank: need a way out

• ✅ Standard RI, regional. You can sell it on the RI Marketplace once it has been active for 30 days, for a 12% fee.
• ❌ EC2 Instance SP: the same price, but after the first 7 days there is no way out.
• ❌ Compute SP, Convertible RI: a lower discount, and no exit either. A Convertible RI can't be sold.

F. "No" to Q1: not 24/7, or not for a whole year

• ✅ On-Demand. Stop the instance when it isn't needed.
• ❌ All four: a Savings Plan bills its commitment every hour, and an RI bills every hour of its term, whether anything runs or not.

This doc's scenario (one t4g.micro, 24/7, Sydney only, might move to t3a) answers "yes" to Q1 and "maybe" to Q3, so it lands on B: Compute SP, 1 yr, No Upfront, committing $0.0083/h. If you rule out t3a for good, it becomes A: EC2 Instance SP for t4g.

Sydney prices, per instance, per month (No Upfront)

Instance	On-Demand $/h	On-Demand /mo	Compute SP 1 yr	EC2 Inst. SP 1 yr	Compute SP 3 yr	EC2 Inst. SP 3 yr
t4g.micro	$0.0106	$7.74	$6.06	$4.89	$4.31	$3.36
t4g.small	$0.0212	$15.48	$12.04	$9.78	$8.61	$6.72
t4g.medium	$0.0424	$30.95	$24.16	$19.49	$17.23	$13.43
t3a.micro	$0.0119	$8.69	$6.79	$5.47	$4.82	$3.72
t3a.small	$0.0238	$17.37	$13.58	$10.95	$9.64	$7.52
t3a.medium	$0.0475	$34.67	$27.08	$21.83	$19.34	$14.96

• Standard RI ≈ EC2 Instance SP and Convertible RI ≈ Compute SP. The RI columns would repeat these numbers.
• t4g costs about 11% less than t3a at every size. Move to t3a only if something needs x86.
• All Upfront takes about 4–5 more points off. For example, a 3 yr EC2 Instance SP for t4g.micro is $0.0040/h ($2.92/mo) All Upfront, against $0.0046/h No Upfront.

Q1 — I only use t4g. Which plans can I choose?

All four. They differ in price and in how you're locked in:

Plan for t4g	1 yr / 3 yr off (No Upfront)	Covers a later t4g.micro → t4g.medium move?	Covers a move to t3a?
EC2 Instance SP, t4g, Sydney	37% / 57%	✅ automatically, up to the $/h you committed	❌ the commitment is wasted
Standard RI, t4g.micro, regional	37% / 57%	⚠️ partly. Size flexibility applies the RI's footprint to the bigger instance (see below)	❌
Compute SP	22% / 44%	✅ up to the $/h you committed	✅
Convertible RI	22% / 44%	⚠️ partly, as with the Standard RI	✅ after a manual exchange

Best t4g-only pick: the EC2 Instance Savings Plan. It costs the same as a Standard RI. It also applies to any t4g size, OS or tenancy without you modifying anything, and it is measured in dollars, so adding a top-up plan later is simple.

Q2 — Convertible RI vs Standard RI: what can I change?

Attribute	Standard RI	Convertible RI
Availability Zone, and scope (zonal ↔ regional)	✅ modify	✅ modify
Size within the same family and generation (t4g.micro → t4g.medium)	✅ modify, only if the total footprint stays the same (Linux, default tenancy)	✅ modify, or exchange
Instance family (t4g → t3a)	❌ never	✅ exchange
OS / tenancy	❌	✅ exchange
Payment option	❌	✅ to more upfront only. No Upfront → Partial/All is allowed. Partial/All → No Upfront is not.
Region	❌	❌ "fixed for the duration of the reservation's term"
Term / end date	❌	❌ the new RI keeps the old end date. Merging RIs with different terms gives a 3 yr RI.
Total value	n/a	Can only stay the same or go up. You pay a pro-rated true-up for any extra.
Exit early	✅ sell it on the RI Marketplace. Needs a bank with a US address, the RI active for 30+ days, and costs a 12% fee.	❌ can't be sold

Footprint rule (both RI types). Sizes are normalised: nano 0.25, micro 0.5, small 1, medium 2, large 4. A t4g.micro RI is 0.5 units, so you can't modify it into a t4g.medium (2 units). If you leave it regional, it still applies its 0.5 units to a running t4g.medium. That covers a quarter of the medium. The other three quarters are billed On-Demand until you buy more.

Convertible exchange example. You have a 1 yr Convertible RI for t4g.medium and 5 months are left. You exchange it for t3a.medium. You get as many t3a.medium reservations as its value covers, rounded up, and pay the true-up for the extra. The new reservation also ends in 5 months. It stays in Sydney.

Q3 — Compute Savings Plans: how they work, what's fixed on day 1, how much to commit

How they work

1. You commit to $X per hour for 1 or 3 years. That figure is spend at Savings Plan rates, not at On-Demand rates.
2. Every hour, AWS goes through your eligible usage, highest discount % first. It charges the Savings Plan rate until it has used up $X.
3. Usage above $X that hour is billed On-Demand.
4. Unused commitment that hour is lost. "Each hour's commitment can only be used within that hour and cannot be carried over." You pay $X every hour, even with nothing running.
5. The order is: RIs first, then EC2 Instance SPs, then Compute SPs.

What is fixed on day 1

Fixed for the whole term	Not fixed
Hourly commitment ($/h). It can't be lowered, cancelled or modified.	Instance family, size, OS and tenancy
Term: 1 yr or 3 yr	Region. Sydney today, anywhere later.
Payment option: No / Partial / All Upfront	Which instances it covers from hour to hour
Start date and end date	How many more plans you buy later. Plans stack.

Way back: you can return a plan if it was bought in the last 7 days, in the same calendar month (UTC), and its commitment is $100/h or less. The limit is 10 returns per calendar year. You get a 100% refund. After that window you're locked in.

How much to commit on day 1

Commit to the floor: what you know will run 24/7 for the whole term. Add a second plan when you scale up. Never commit for a size you haven't moved to yet.

You run today	Commit (Compute SP, 1 yr, No Upfront)	Cost	What it covers
1 × t4g.micro	$0.0083/h	$6.06/mo, $72.71/yr	100% of the micro
…you later move to t4g.medium	the same $0.0083/h	—	25% of the medium ($0.0083 ÷ $0.0331). Buy a second plan for about $0.0248/h.
…you later move to t3a.micro	the same $0.0083/h	—	89% of the micro ($0.0083 ÷ $0.0093). The rest is On-Demand.

• The usual mistake is committing the On-Demand price ($0.0106) instead of the Savings Plan rate ($0.0083). That over-commits by about 28%, and the extra 28% is wasted every hour.
• 3 yr No Upfront: the commitment for one t4g.micro is $0.0059/h ($4.31/mo).
• With All Upfront you pay the commitment × the hours in the term on day 1. For example, $0.0077/h × 8,760 h ≈ $67.45 for a 1 yr plan covering one t4g.micro.
• After a new instance has run for a week or two, check the commitment AWS recommends in Billing → Savings Plans → Recommendations / Purchase Analyzer before you buy.

Q4 — EC2 only, always Sydney: EC2 Instance SP vs Standard RI vs Convertible RI

	EC2 Instance SP	Standard RI	Convertible RI
Discount, t-family, 1 yr / 3 yr (No Upfront)	37% / 57%	37% / 57%	22% / 44%
You commit to	$/hour	N × one instance type	N × one instance type
Change size	✅ automatic	⚠️ regional RI flexes by footprint. To resize the RI itself, modify it and keep the footprint the same.	⚠️ same as Standard, or exchange
Change family (t4g → t3a)	❌	❌	✅ manual exchange, value must stay the same or go up
Change OS / tenancy	✅ automatic	❌	✅ exchange
Change region	❌	❌	❌
Capacity reservation	❌	✅ only if zonal	✅ only if zonal
Upsize later	buy another small plan	buy another RI	buy another RI
Exit	return within 7 days only	sell on the Marketplace (US bank, 12% fee)	❌ none
Effort	none	low	you have to remember to do exchanges

What this means for you:

• The EC2 Instance SP beats the Standard RI. The price is the same and it has fewer rules. Pick a Standard RI only if you want a zonal capacity reservation or the Marketplace exit, and that exit needs a bank with a US address.
• Compute SP beats the Convertible RI. The price is the same, and it switches family, size and OS without manual exchanges. It also gets you region freedom, which you don't need.
• So the real choice is EC2 Instance SP vs Compute SP: about 15 points more discount, against keeping the option to move to t3a.

Break-even: what if I lock to t4g and then move to t3a?

1 yr No Upfront, one micro. On the t4g plan, the t4g commitment is wasted after the move and the t3a is billed On-Demand. On the Compute SP, the plan keeps covering about 89% of the t3a.

Move to t3a.micro after…	EC2 Instance SP (t4g) total	Compute SP total
never	$58.69	$72.71
month 11 (90%)	$69.12	$73.83
month 10 (85%)	$74.33	$74.39
month 6 (50%)	$110.81	$78.31
month 3 (25%)	$136.88	$81.11

The EC2 Instance SP only wins if you'd move in roughly the last 15% of the term, or never. A t4g.medium → t3a.medium move breaks even at the same point (about 85%). At t4g.micro size the gap is about $14/yr, so the Compute SP's insurance is cheap.

What none of the four discounts

These show up on the same bill but are always charged at full price:

• Burstable CPU credits. t4g, t3a and t3 launch in unlimited mode. CPU use above baseline, averaged over 24 h, is billed as surplus credits. The Sydney Savings Plans price file has no rate at all for CPUCredits usage.
• Public IPv4 address. It is billed per hour on its own line. At t4g.micro size that's a big share of the bill.
• EBS volumes, snapshots, data transfer.
• Spot usage. Savings Plans don't apply to Spot.

Sources

• AWS Price List API: EC2 offer file ap-southeast-2 and Savings Plans file ap-southeast-2/20261003071546 (pulled 2026-10-05)
• Compute Savings Plans and Reserved Instances (comparison table)
• How Savings Plans apply to your usage
• Returning a purchased Savings Plan · Quotas
• Exchange Convertible Reserved Instances
• Modify Reserved Instances (footprint and normalisation)
• Sell in the Reserved Instance Marketplace
• Unlimited mode for burstable instances