About 4-week billing (28-day option period)

4-week billing (sometimes called 28-day option period or Wochen-Tarif) is the German prepaid market convention of charging the customer every 28 days rather than every calendar month. It is a common point of consumer confusion because the headline price reads like a monthly fee.

A tariff advertised as EUR 9.99/month usually renews every 28 days, which means 13 billings per year instead of 12. The true annual cost is EUR 9.99 × 13 = EUR 129.87/year, not EUR 119.88. The same logic applies to every German prepaid brand using 4-week cycles: ALDI TALK, LIDL Connect, NORMA connect, KAUFLAND MOBIL, ja! mobil, Penny Mobil, congstar, Telekom prepaid, Vodafone CallYa.

To compare prices correctly, always annualise both cycles:

• 4-week price × 13 = annual cost
• Monthly price × 12 = annual cost
• 6-month price × 2 = annual cost
• Annual price = annual cost

The German contract and flex market uses true monthly billing instead: fraenk (EUR 10/month = EUR 120/year), 1&1 All-Net-Flat, Blau Flex, N26 SIM, and all 24-month contracts. So a fraenk at EUR 10/mo is actually cheaper per year than a 4-week tariff at EUR 8.99/4w (EUR 120 vs EUR 116.87) despite the higher headline price.

This billing convention is inherited from GSM-era prepaid cards where the validity period was 28 days. The convention persisted even after monthly billing became technologically trivial. Some consumer groups have lobbied for clearer disclosure but Bundesnetzagentur has not yet mandated a change.