Another thing to note that's specific to the 403(b)/solo 401(k) combo (as opposed to the 401(k)/solo 401(k) combo where this doesn't apply) is is that not only is the salary deferral limit combined as it is with all workplace plans, but the overall limit (around $66k as of 2024 I think?) is also combined. This is because of some obscure law that considers both 403(b) and solo 401(k) to be under control of the individual. This probably isn't a problem unless you have some combination of very high income at your job and/or business, very good employer match, or you make mega-backdoor Roth contributions through your 403(b) or solo 401(k) such that you contribute up to the overall limit across both plans.