Short answer: a dynamic number insertion pool needs one number for every visitor who is holding one at your busiest moment. Work it out as:
numbers ≈ tracked visitors in your peak hour × (minutes on site + lease + cooldown) ÷ 60, plus about 20%
With Edesy's defaults (30-minute lease, 30-minute cooldown) and a 3-minute average visit, each visitor ties up a number for about 63 minutes. 40 tracked visitors in the peak hour need about 51 numbers. The free call tracking number pool calculator does this for your own traffic and shows the monthly cost.
Why a visitor holds a number for an hour
Dynamic number insertion works because only one visitor holds a given number at a time. If two people saw the same number at once, you couldn't tell which one called. So each number goes through three stages for every visitor:
| Stage | Default on Edesy | Why it exists |
|---|---|---|
| On the page | As long as the tab is open (renewed every 60 s) | The visitor may call while reading |
| Lease | 30 minutes after they leave (5 to 240) | Many people call after closing the tab |
| Cooldown | 30 minutes | A late call still reaches the right visit before anyone else sees the number |
A call during the lease is an exact match. A call during the cooldown is a grace match, credited to the same visit. The full rules are in Attribution Rules.
Worked examples
All with 3 minutes on site, so 63 minutes held per visitor at the defaults:
| Tracked visitors in peak hour | At once (rounded up) | With 20% headroom |
|---|---|---|
| 10 | 11 | 14 |
| 25 | 27 | 33 |
| 40 | 42 | 51 |
| 100 | 105 | 126 |
| 250 | 263 | 316 |
The 20% headroom is the same margin the Edesy pool health view uses when it suggests a size: peak concurrent leases times 1.2.
Use the peak hour, not the average
The most common mistake is dividing monthly visits by the hours in a month. A site with 30,000 visits a month averages about 42 an hour, but if Sunday 11 a.m. brings 120 because a property launch ad is running, a pool sized for 42 will be full for most of that peak. Pull sessions by hour from your analytics, take a normal busy week, and use its busiest hour.
Three ways to need fewer numbers
1. Track paid traffic only
This is the biggest lever. In paid-only mode, only visits with an ad click ID (gclid, gbraid, wbraid, fbclid, msclkid) or a paid utm_medium such as cpc get a tracking number. Organic and direct visitors keep your normal number. If a quarter of your peak-hour visits come from ads, 40 visitors becomes 10 tracked visitors, and the pool drops from 51 to 14 numbers.
Ad traffic is also where attribution pays for itself, because it decides where you spend money. Tag non-Google campaigns with the UTM link builder so they count as paid.
2. Shorten the lease and cooldown
At 15 + 15 minutes instead of 30 + 30, each visitor holds a number for 33 minutes, and 40 tracked visitors need about 27 numbers. The trade-off: someone who calls 40 minutes after leaving will no longer be matched to their visit. If your buyers usually call within minutes (food, emergency services, taxis), shorter windows are fine. If they compare options first (property, education, healthcare), keep the defaults.
3. Split pools by site
Leases are per pool. A small microsite doesn't need to share a pool sized for your main site's peak. Give each its own pool so each is sized for its own traffic, and so reports stay separate.
What happens when the pool runs out
On Edesy you choose:
| Setting | Visitor sees | Result |
|---|---|---|
| Show the normal number (default) | Your site's own number | Calls from those visitors aren't tracked; every other call stays accurate |
| Reuse the oldest lease | A number someone else may still hold | Everyone gets a number, but some calls may be credited to the wrong visit |
We recommend the default. A pool that is occasionally full loses a few data points; a pool that reuses leases quietly corrupts your reports.
Check your size after a week
Once the snippet is live, the pool's Health tab shows the numbers in use right now, peak concurrent leases, visits that found the pool full, attributed calls and a suggested pool size. If the suggestion is above your current size, add numbers. If peak usage stays well below your pool, you can remove some. See Number Pools.
What a pool costs
There is no tracking fee on Edesy. You pay:
| Cost | Price |
|---|---|
| Each pool number | Its normal monthly rental (see call tracking pricing) |
| Calls to tracking numbers | Rs 1.00 per minute, the forwarding rate |
| Reports, CSV exports, Google Ads CSV, webhook | Included |
Prices exclude 18% GST. Because rental is per number, pool size is the main cost driver, which is one more reason to start with paid traffic only.
FAQ
How many tracking numbers do I need?
Roughly your tracked visitors in the busiest hour multiplied by (minutes on site + lease + cooldown) divided by 60, plus about 20%. With 40 tracked visitors, 3 minutes on site and 30-minute lease and cooldown, that is about 51 numbers.
Why use daily or monthly traffic at all?
You shouldn't. A pool runs out at your busiest moment, so size it from the peak hour. Monthly visits divided by hours in the month hides the spike you need to cover.
What happens if the pool is too small?
On Edesy, by default, visitors who arrive when every number is in use see your normal number and their calls are not tracked. Attribution for everyone else stays accurate.
Can I start with a small pool?
Yes. Track paid traffic only, start with the calculator's suggestion, and watch the pool's Health tab for visits that found the pool full and the suggested pool size.
Does each number cost extra for tracking?
No tracking fee. Each pool number has its normal monthly rental, and calls cost Rs 1.00 per minute at the forwarding rate. Prices exclude 18% GST.