How are my credits counted?
1 min read · Last updated June 2026
Each image you optimize uses one credit, no matter how many output formats SlashImage generates from it. Creating WebP and AVIF copies does not cost extra credits; those are included in the one credit for that image.
One image, one credit
When SlashImage optimizes an image, it makes a WebP and an AVIF copy of it. All of that is a single credit. You are charged for the image you optimized, not for the extra formats that make your pages fast.
Thumbnail sizes each use a credit
WordPress creates several thumbnail sizes from every image you upload (a thumbnail, medium, and large version, plus any sizes your theme registers). Each of those sizes is a separate image, so optimizing them uses one credit each.
To cap how much a single site can use, give it a sub-key with its own monthly credit limit. That limit is a ceiling within your account's overall allowance, not extra credits.
Counted across your account
Credits are counted per account, not per site. If you use the same API key across several sites, they all draw from the same monthly total, so two busy sites use your credits twice as fast as one. See Can I use one API key on multiple sites?.
When it resets
Your allowance resets each month. On the Free plan it resets on the first of the month; on a paid plan it resets with your billing cycle.