Angle Compensation Calculator for Archery

Every angled shot, up or down, plays shorter than the distance you ranged. Not longer uphill and shorter downhill: shorter both ways, by exactly the same amount for the same angle. This calculator applies the cosine correction and shows you how many yards you would have aimed away without it.

The formula and why it works

True horizontal distance equals line of sight distance multiplied by the cosine of the angle. At 40 yards down a 30 degree slope, cosine 30 is 0.866, so the shot plays as 34.6 yards. Use your 35 yard pin, not your 40.

The reason is that gravity pulls straight down and nothing else. An arrow in flight is being bent downward at a constant rate the whole time, and how far it falls depends only on how long it is in the air. Over a slanted path, only the horizontal component of that path contributes to the sight correction you need, because the vertical portion of the arrow's travel is already along the same line gravity is acting on.

That is why the sign of the angle does not matter. Cosine of positive 30 degrees and cosine of negative 30 degrees are both 0.866. Uphill and downhill shots at the same angle require exactly the same correction, and both require you to aim for a shorter distance. The widespread belief that you hold high uphill is the single most reliable way to shoot over an animal from a ridge.

Angle correction chart

The multiplier column is the cosine of the angle. Multiply your ranged distance by it, or read the yardage columns directly.

Nobody estimates a 27 degree angle by eye with an animal in front of them. Angle-compensating rangefinders exist because this correction is real, is arithmetic, and cannot be done under pressure. Any rangefinder marketed for bowhunting will read the angle with an inclinometer and return the corrected yardage in the same display, and the archery-specific models go further by factoring in your arrow speed. It is the accessory that most directly converts into hits.

Treestands: close shots are the steep ones

The intuition most hunters carry is that a higher stand means a bigger correction. What actually drives the angle is the ratio of height to distance, so a stand becomes steep as the shot gets closer, not as the stand gets taller. Distances below are the ranged line of sight figure, which is what a non-compensating rangefinder shows you.

From a 20 foot stand, a 10 yard shot is a 42 degree angle and plays as roughly 7.4 yards. Aiming at 10 would put the arrow high by several inches on a target that small. Meanwhile the 40 yard shot from the same stand needs less than a yard and a half of correction. The lesson for stand hunters is that the close shot is the one that needs the discipline, which is the opposite of what most people expect.

When it matters and when it does not

• Under 15 degrees: correction is under 4 percent. At 30 yards that is about a yard, well inside normal aiming error. Ignore it.
• 15 to 25 degrees: 3 to 10 percent. Worth applying past 25 yards, and worth applying always if you are shooting at small vitals.
• 25 to 40 degrees: 10 to 23 percent. This is now the largest single source of error in the shot, larger than your group size.
• Over 40 degrees: 23 percent and up, and increasingly steep in both senses. Compensation is mandatory, and so is a hard look at whether the shot geometry gives you an acceptable angle through the animal at all.

Doing it in your head, when you have to

Batteries fail and rangefinders get left in packs, so it is worth carrying two approximations that are close enough to shoot on. The first is the ten and twenty rule: at roughly 25 degrees take 10 percent off the ranged distance, and at roughly 40 degrees take a quarter off. Both land within about two percent of the true cosine, which across normal archery distances is well inside the size of a vital area.

The second is a fixed stand card. Because your stand height does not change during a sit, you can work the corrections out once, on the ground, and tape four numbers to your bow limb: the corrected yardage for 10, 20, 30 and 40 yards from that specific height. It takes two minutes with the calculator above and it removes arithmetic from the moment where you have the least capacity for it.

What neither shortcut replaces is knowing the raw distance in the first place. A ten percent correction applied to a distance you guessed badly is still a bad number. If you only carry one tool up the tree, carry the one that measures.

Form on angled shots

The arithmetic is the easy half. The harder half is that bending at the waist rather than dropping the bow arm is what keeps your anchor, your peep alignment and your shoulder geometry intact. Dropping the bow arm alone changes the relationship between your anchor and the string, and it moves impact independently of any distance correction. Practise steep shots from the height you actually hunt from, because the correction chart cannot fix a collapsed form.

It is also worth knowing what your arrow does at close range from elevation. A steeply angled close shot combined with a heavy, slow arrow leaves very little margin, so it is worth confirming what your setup produces with the kinetic energy calculator and checking your trajectory assumptions with the sight tape calculator.

Related tools

• Sight tape calculator: pin gaps and how far your sight can reach
• Arrow speed calculator: a flatter arrow forgives range errors
• Arrow FOC calculator: heavy front ends steepen trajectory
• Best archery rangefinders: the tool that does this in the field