AWS EC2: price of maxed out burstable instance in unlimited mode

The T instance families, namely T2, T3, T3a, and T4g are burstable. They are designed for low to moderate CPU utilization with intermittent heavy spikes. At times of low CPU utilization below a AWS-defined baseline, your instance collects credits that later can be spent on times of high CU utilization.

A credit gives you one minute of 100% CPU. The credits earned per hour are specified here: T2, T3 and T3a, T4g.

A burstable instance has a setting called "Credit specification" with the two options "standard" and "unlimited". This setting decides what happens if your instance runs out of credits: in standard mode, the CPU is gradually throttled to the baseline; in unlimited mode, the missing credits cost you surplus charges. See also the description of the standard mode and unlimited mode and the EC2 pricing page.

The surplus charge is 0.05 $ per hour and vCPU. So, a maxed out instance costs you (vCPUs - (credits earned per hour / 60)) * 0.05 per hour.

At the time of writing (2021-08-30), this gives for Linux (L) and Windows (W):

Type	Base $/hr (L)	Base $/hr (W)	Max $/hr (L)	Max $/hr (W)
t2.nano	0.00670	0.00900	0.05420	0.05650
t2.micro	0.01340	0.01800	0.05840	0.06300
t2.small	0.02680	0.03600	0.06680	0.07600
t2.medium	0.05360	0.07160	0.13360	0.15160
t2.large	0.10720	0.13520	0.17720	0.20520
t2.xlarge	0.21440	0.25540	0.36940	0.41040
t2.2xlarge	0.42880	0.49080	0.76130	0.82330
t3.nano	0.00600	0.01060	0.10100	0.10560
t3.micro	0.01200	0.02120	0.10200	0.11120
t3.small	0.02400	0.04240	0.10400	0.12240
t3.medium	0.04800	0.06640	0.12800	0.14640
t3.large	0.09600	0.12360	0.16600	0.19360
t3.xlarge	0.19200	0.26560	0.31200	0.38560
t3.2xlarge	0.38400	0.53120	0.62400	0.77120
t3a.nano	0.00540	0.01000	0.10040	0.10500
t3a.micro	0.01080	0.02000	0.10080	0.11000
t3a.small	0.02160	0.04000	0.10160	0.12000
t3a.medium	0.04320	0.06160	0.12320	0.14160
t3a.large	0.08640	0.11400	0.15640	0.18400
t3a.xlarge	0.17280	0.24640	0.29280	0.36640
t3a.2xlarge	0.34560	0.49280	0.58560	0.73280
t4g.nano	0.00480		0.07480
t4g.micro	0.00960		0.08960
t4g.small	0.01920		0.03920
t4g.medium	0.03840		0.11840
t4g.large	0.07680		0.16680
t4g.xlarge	0.15360		0.19360
t4g.2xlarge	0.30720		0.70220

As you can see, especially small instances cost you multiple times the base price if maxed out, while bigger instances get a little more expensive than their C5a counterparts. However, C5a instances give you 3.3 GHz per CPU, while T3a for example gives you only 2.2 GHz.

TL;DR: If you need a lot of CPU continuously, don't use burstable instances. Use one of the C families instead!