FOC Guide for Bowhunting Arrows: How Front of Center Affects Accuracy and Penetration
Front of center (FOC) is how far the balance point sits ahead of the shaft midpoint, as a percent of cut length. That number is what keeps a fixed blade from planing and what puts weight into the animal. Inserts and points raise it. Wraps, vanes, and lighted nocks lower it. Type a measured balance and the number updates. For a TitleX build estimate without a scale, use the 3D custom arrow builder — it uses this same formula from GPI, cut, insert, point, wrap, and vanes.
FOC calculator
Formula: 100 × (balance from nock − length / 2) / length. Cut length is nock throat to the end of the shaft, not including the point.
- FOC
- —
- Midpoint
- —
- Balance from nock
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Enter cut length and the balance point.
Estimate FOC on a TitleX build in the 3D custom arrow builder
How to measure
- Finished cut length: nock throat to the end of the shaft. Do not include the point.
- Balance the arrow on a knife edge or a dedicated FOC jig. Mark the spot.
- Measure from the nock throat to that mark. If you measured from the point end, switch the calculator to that mode.
How FOC affects accuracy
A hunting head is a wing. If the balance is too far back, the head can plane and the group opens. Enough FOC keeps the point pulling the shaft. Rough bands: under 8% is often too rear-heavy for a fixed blade; 10–15% is a common hunting window. Those are starting talk. Confirm with the head you hunt with.
How FOC affects penetration
More weight up front usually hits harder and tracks straighter through tissue after the hole. Past about 15% can penetrate well and get pickier to tune. GPI still matters: a heavy TX-5 at moderate FOC can out-penetrate a light shaft with a huge FOC number. Pick shaft GPI on the TitleX spine chart, then re-check this calculator on the finished arrow.
Related resources: arrow calculators, kinetic energy calculator, arrow spine chart, 3D custom arrow builder, broadhead tuning, draw length calculator.