Start and End Time of a Data Transfer
Calculator for the time at the start or end of a transfer at a given duration, or size and transfer speed. The data size and transfer speed can be entered to calculate the transfer time. If at transfer time, start time and end two of the three values are entered, the third value will be calculated. At the time of the transfer end, the value at d means days, if there is a 1, the transfer ends the next day. Enter times if 24-hours-format.
Example: 4 gigabytes are transferred with a speed of 2 Mbit per second, this takes 4 hours, 26 minutes and 40 seconds. If the transfer starts at 21:15, it ends the next morning at 1:41 and 30 seconds.
This calculation is valid if the transmission speed is constant, but also if the specified value exactly matches the average transmission speed. In practice, however, this is usually not the case. Therefore, the user should not necessarily rely on the calculated end time being adhered to and should allow for a time buffer.
The calculation of transmission time is based on the formula Duration = File size / Transmission rate. The file size is converted into bits using 8 bits per byte, while the transmission rate is given in bits per second. For example, 1 GB = 8000 Mbit, which at 2 Mbit/s results in 4000 seconds (approximately 1.11 hours). However, fluctuations due to protocol overhead (as with TCP/IP), packet loss, or network latency, which reduce the effective rate, are practically relevant. Furthermore, parallel transmissions, router prioritization, or ISP throttling affect the speed. With wireless connections (Wi-Fi, mobile networks), sources of interference such as signal strength or other interference can further reduce the rate. The theoretical maximum speed is rarely achieved. Realistically, only 70 to 90 percent of the nominal value is often reached. For precise planning, measurements of the actual throughput rate (e.g., via a speed test) should therefore be used as a basis.
Last updated on 12/16/2025. Author: Jürgen Kummer
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