Log Growth Calculator

Estimate application log directory growth rate and days until disk capacity is reached.

About Log Growth Calculator

Assuming a roughly constant daily growth rate, a log file's size at any future day is simply its current size plus the daily growth multiplied by the number of days elapsed — a linear projection. Rearranging that same relationship to solve for time gives the number of days until the log reaches any chosen size threshold, whether that threshold represents a monitoring alert level or the physical capacity of the partition it lives on, which is useful for scheduling log rotation or cleanup before a threshold is breached rather than reacting after the fact.

Formulas

Projected size at day n

size_at_day_n = initial_size + daily_rate × n

S_0: initial size
r: daily growth rate
n: number of days

Days until threshold

days = (threshold − initial_size) / daily_rate

T: threshold size
S_0: initial size
r: daily growth rate

Worked example

With the default values below, Log Growth Calculator returns Projected Size at End of Period of 2,000.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Current Log Sizeminimum 0 MB: 500 MB
Daily Growth Rateminimum 0 MB/day: 50 MB/day
Projection Periodminimum 1 days: 30 days
Size Threshold to Watch Forminimum 0 MB: 5,000 MB

Results

Projected Size at End of Period: 2,000.00 MB
Threshold Status: Threshold reached in approximately 90 days
Total Growth Over Period: 1,500.00 MB

Step by step

1Values used
2Projected size at day n
3Days until threshold
4Projected Size at End of Period= 2,000.00 MB
5Threshold Status= Threshold reached in approximately 90 days
6Total Growth Over Period= 1,500.00 MB

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or fees or charges into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why might actual log growth deviate from this linear projection?

Real log volume often correlates with traffic or error rates, which vary by day of week, seasonal events, or incidents — a sudden bug causing repeated error logging can spike growth far above the historical average rate used in a linear projection, so treat this as a planning estimate rather than a guarantee.

How can I measure a log file's actual daily growth rate?

Sample the file size with `stat -c%s /path/to/log` (or `du`) at the same time on consecutive days and take the difference, or average the difference over a week to smooth out day-to-day variance before feeding it into a growth projection.

What should I do once I know when a threshold will be reached?

Set up or tighten logrotate rules to cap growth before the threshold date, add monitoring alerts at an earlier checkpoint (e.g. 80% of the threshold) to catch acceleration in the growth rate, or route logs to centralized storage with its own retention policy.