Pay in Definition 1 of 3Pro Tip 1/3Monetary Context Pay in is often used in banking or financial contexts for actions involving money handling. She went to the bank to pay in some cash she had saved. Pro Tip 2/3Regular Payments Use 'pay in' for regular, often monthly, deposits, like a salary, to a savings or checking account. On the 1st, I'll pay in my paycheck. Pro Tip 3/3Specific Amounts It can imply depositing a specific amount, as planned or agreed upon, not just any sum. I will pay in the exact amount needed for the bill.