If you travel using the e-purse balance on your OV-chipkaart then a temporary boarding rate of 4 euros is debited from your OV-chipkaart when you check in. When you check out, the fare for the trip is automatically calculated and deducted from the boarding rate and the remainder is credited back to your OV-chipkaart.
The boarding rate of 4 euros is a deposit. This amount has been established at the national level and is the same for all city and regional transport companies in the Netherlands.
Note: the boarding rate is different for the national rail system (NS). More information is available on the NS website.
When you travel with a balance on your e-purse, you pay a base rate and a fixed amount per kilometer. The kilometers are accurately rounded up to 50 meters. You pay for the distance you travel. The base rate is a fixed amount and applies to all city and regional transport (bus, tram and metro). If you transfer within 35 minutes of checking out into another bus, tram or metro, you do not pay the base rate again.
When you check out, your fare is settled against the boarding rate of four euro. If the fare for your trip is less than four euro then the remainder is credited back to your card.