For more information about health insurance, pensions and taxes, see the pages ‘Working in the Netherlands’
If you have a part-time job in the Netherlands, you have to pay a health insurance contribution to your Dutch health insurance (zorgverzekeraar). This amounts to approximately € 85 to € 115 per month. If you have no income or a small income, you can apply for an subsidy (zorgtoeslag). You can read more about this here and on the website of the Dutch tax office (only in Dutch)
. If you only have a part-time job in Germany, you are always subject to German social security.
If you have a part-time job in the Netherlands and also in Germany, e.g. a mini-job, you are usually subject to German social insurance. Read more about working in two countries here.