Plantar Fasciitis vs. Achilles Tendonitis: Which One Do You Have?
The quickest way to tell them apart is to find where it hurts. Plantar fasciitis hurts on the bottom of your heel and is usually worst with your first steps after resting. Achilles tendonitis hurts at the back of your heel, or along the tendon just above it, and it is stiff and sore when you start moving. Both are overuse problems, and they often show up together.
Here is how to sort out which one you have, why they get mixed up, and what to do about each.
Where the pain is
This is the most useful clue, and most people have never paid attention to it.
- Plantar fasciitis: the bottom of the heel, sometimes spreading into the arch. Pressing on the inside edge of the heel bone on the underside is often tender.
- Achilles tendonitis: the back of the ankle. It can sit along the thick cord a few finger-widths above the heel, or right where the tendon meets the heel bone. The tendon may feel thick or tender when you squeeze it gently from the sides.
When it hurts
| Plantar fasciitis | Achilles tendonitis | |
|---|---|---|
| Location | Bottom of the heel, sometimes the arch | Back of the heel or the tendon above it |
| First steps after rest | Sharp and worst, then eases as you walk | Stiff and sore, loosens up with movement |
| After sitting a while | Flares again on standing | Stiffness returns |
| Pushing off, hills, stairs | Can hurt, mainly under the heel | Often the clearest trigger |
| Touch test | Tender on the underside of the heel | Tender and sometimes thickened along the tendon |
| Usual cause | Load on the foot's arch tissue, tight calves, a sudden jump in activity | Repeated load on the tendon, tight calves, a sudden jump in activity |
What is happening inside your foot
The plantar fascia is a thick band of tissue under your foot, running from the heel bone toward your toes. It supports your arch, and when it is overloaded it becomes irritated where it attaches to the heel.
The Achilles tendon is the strong cord that connects your calf muscles to the back of your heel bone. It takes a lot of force with every step, and it can become irritated in the middle of the cord or where it attaches to the bone.
Different tissue, different spot. But both hang off the same calf muscles, which is why they get confused.
Why they get mixed up, and why you can have both
Tight calves pull on the Achilles at the back and, through the foot, add load to the plantar fascia underneath. So the same triggers show up for both: a jump in running mileage, a new job on your feet, stiff shoes, or a flat or very high arch. It's common for someone to have both at once, and for heel pain that doesn't improve with plantar fasciitis care to turn out to involve the Achilles too.
If you also have pain on the back of the heel that gets worse when a shoe rubs it, read Heel Bursitis vs. Plantar Fasciitis. The bursa between the tendon and the heel bone is a third possibility.
What usually helps with each
Much of the early advice is the same. Cut back on whatever started it, wear supportive shoes, and build up activity gradually instead of jumping back in.
- Plantar fasciitis: arch support, calf stretching and stretches for the underside of the foot are common starting points. See Plantar Fasciitis Relief: Why Infrared Socks Work Better.
- Achilles tendonitis: the tendon generally responds to a gradual, controlled loading plan rather than rest alone or aggressive stretching. A physical therapist can set one up. See Achilles Tendinosis Treatment: What Works and Achilles Pain Relief.
Where infrared socks fit
ACCAPI makes an Energy Wave sock for each problem. Both combine infrared fiber, which absorbs your body heat and re-emits it as far infrared energy in the 5–20 micron range, with light compression and integrated support taping.
- The Plantar Fasciitis Socks have taping placed at the arch and the underside of the foot.
- The Achilles Socks have taping positioned over the Achilles area.
They are comfortable support to wear while you're on your feet. They don't diagnose anything and they aren't a replacement for care. Want to know what the fiber is? See infrared fibers explained.
When to see someone
Most heel pain improves with sensible footwear, load changes and patience. Get it checked if the pain is severe, if there is swelling, redness or numbness, or if it isn't improving. A podiatrist or physical therapist can usually tell the two apart in one visit, sometimes with imaging. A sudden pop at the back of the ankle followed by trouble pushing off needs urgent attention.
Frequently asked questions
How do I know if my heel pain is plantar fasciitis or Achilles tendonitis?
Location is the biggest clue. Plantar fasciitis hurts on the bottom of the heel and is usually worst with the first steps after rest. Achilles tendonitis hurts at the back of the heel or along the tendon just above it, and it is stiff and sore at the start of activity.
Can you have plantar fasciitis and Achilles tendonitis at the same time?
Yes. Tight calf muscles load both the Achilles tendon and the plantar fascia, so the two often show up together. If one problem isn't improving, it's worth asking whether the other is involved.
Is Achilles pain in the back of the heel or the bottom?
Achilles pain is at the back of the heel or in the cord-like tendon above it. Pain on the bottom of the heel or arch points toward the plantar fascia instead.
Why is plantar fasciitis worse in the morning?
The plantar fascia tightens while you rest. The first steps stretch it again, which is when it hurts most. It often eases as you walk and returns after you've been sitting.
Should I stretch for Achilles tendonitis the way I do for plantar fasciitis?
Calf stretching is common advice for both, but an irritated Achilles tendon doesn't always like aggressive stretching, especially where it meets the heel bone. Ask a clinician or physical therapist which exercises suit your case.
Can infrared socks help with either one?
ACCAPI makes an Energy Wave sock for each: the Plantar Fasciitis Socks have integrated arch and plantar support taping, and the Achilles Socks have taping positioned over the Achilles area. Both pair infrared fiber with light compression. They are comfortable support to wear while you're on your feet, not a diagnosis or a treatment.
When should I see a doctor about heel pain?
See someone if the pain is severe, comes with swelling, redness or numbness, or isn't improving with rest and sensible footwear. A sudden pop at the back of the ankle with trouble pushing off needs urgent attention, because it can mean a ruptured Achilles tendon.
