# The Merge TTD Goal: find a TTD value which is hit after the Bellatrix mainnet upgrade but before the end of September. If the hashrate drops significantly, we can make a call to override TTD after Bellatrix. ## Strategy for estimating TTD To set the Total Terminal Difficulty value for The Merge, we will first predict the total difficulty value at given dates and then tweak it considering hashrate changes. To determine when the TTD value will be reached, [polynomial regression approach](https://ethresear.ch/t/predicting-ttd-on-ethereum/12742) can create an estimation with reasonable precision. These projections are based on data from the previous four weeks and were produced using the [prediction tool](https://github.com/taxmeifyoucan/predict_ttd/). However, the accuracy is totally dependent on future hashrate volatility. The TTD date may be off by a few days if the hashrate changes significantly and with sufficient time in advance. Let's examine the network's hashrate to establish expectations. ### Hashrate trends In the past months, hashrate averaged around 1PH/s and peaked in May at at 1.126 PH/s. After a sharp decline in June, it started to gradually recover and is now holding at about 900TH/s (average, effective hashrate). Last month it oscillates between 950TH/s and 780TH/s (spikes), with daily variations being no greater than 5%.  Hashrate adjustes based on profitability of mining which corelates with ETH price. Although hashrate is not entirely reliant on price fluctuations, it does respond to them. Here is the ETH price and hashrate since January projected into one chart:  Since hashrate indicates difficulty that must be overcome over time, we can determine the precise amount of hashrate required in the network to achieve TTD at a particular time. [This script](https://gist.github.com/taxmeifyoucan/92f1673b45c82b1764002b276bbfb157) calculates and visualizes how much hashrate is needed to achieve given TTD at a period of time - during September. Here is a visualization where you can see the trend clearly over a bigger time frame. It shows the amount of hashrate required (axis x) to achieve example TTD value at a period of time (y axis). The red portion of the curve represents September, when The Merge may take place.  The shape practically indicates that significantly greater hashrate is required in the first part of the month. This offers more "protection" against hashrate increases in the initial days but then necessary hashrate drops slower. The slow decline can make it painful to achieve TTD if hashrate drops significantly. With [DAG size](https://minerstat.com/dag-size-calculator) reaching 5GB and potential pushback from miners, we have to count on having enough space for a hashrate decline. For this reason, default predicted values are rounded down in the following estimations. ## Scenario 1 estimations Scenario 1, Bellatrix happens on August 31st. | Event | Expected date | | ----------------------------------- | ------------- | | Bellatrix on mainnet | August 31 | | Merge TTD hits | September 15 | Predicted TD to be reached at September 15 noon UTC is between `58774877561390694400000` and `58834281007084994560000`.  To make a nicer and slightly lower number, we can round this down to `58750000000000000000000`. This number would be achieved with only like 10 hours difference. Here is a chart which visualizes the amount of hashrate needed to achieve this TTD during September.  You can see the hashrate necessary to achieve the TTD value drops from around 1400TH/s (23% above hashrate ATH) at September 1 to around 623TH/s by the end of September (29% drop from current hashrate). The red dotted line represents the current hashrate average and intersects the blue curve at September 15, estimated date for the TTD. The next chart plots the necessary hashrate in percentual change compared to the current hashrate which is marked with the red dotted line at 0.  Here is a table to summarize these projected values and compare then to hashrate ATH and current value. | Date | Hashrate needed | ATH | Current | | ------ | --------------- | ----- | ------- | | Sep 1 | 1392 TH/s | +23 % | +58 % | | Sep 8 | 1073 TH/s | -4 % | +22 % | | Sep 15 | 872 TH/s | -22 % | +0 % | | Sep 22 | 735 TH/s | -34 % | -16 % | | Sep 30 | 623 TH/s | -44 % | -29 % | If we count on a maximum 30% hashrate drop, TTD will be achieved by the end of September. If we want to prepare for a bigger drop, TTD has to be set even lower. The following table lists other TTDs to consider, when they are expected to be reached, what hashrate would be needed to achieve it at Bellatrix and what % drop from current hashrate we can expect. | TTD | Expected date | Hashrate at Bellatrix | Drop by The Merge | Drop by Sep 30 | | ----------------------- | ------------- | --------------------- | ----------------- | -------------- | | 58600000000000000000000 | September 13 | 1318 TH/s | 5% | 32% | | 58480000000000000000000 | September 11 | 1260 TH/s | 10% | 35% | | 58300000000000000000000 | September 9 | 1171 TH/s | 16% | 40% | | 58190000000000000000000 | September 7-8 | 1117 TH/s | 20% | 43% | ## Scenario 2 estimations Scenario 2, Bellatrix on September 6. | Event | Expected date | | ----------------------------------- | ------------- | | Bellatrix on mainnet | September 6 | | Merge TTD hits | September 20 | The predicted TD to be reached at September 20 noon UTC is between `59155429252944363520000` and `59227132692074332160000`.  Rounding it down to `59100000000000000000000` makes around 16 hours difference. The next chart plots how much hashrate is needed to achieve this TTD during period September 6 - October 7.  The hashrate necessary to achieve the TTD value drops from 1290TH/s (14% above hashrate ATH) at Bellatrix, Sept 6 to around 700TH/s by the end of September 30 (20% drop from current hashrate). The red dotted line represents the current hashrate average and intersects the blue curve at September 19-20.  | Date | Hashrate needed | ATH | Current | | ------ | --------------- | ----- | ------- | | Sep 8 | 1205 TH/s | -7 % | +37 % | | Sep 14 | 980 TH/s | -12 % | +11 % | | Sep 22 | 826 TH/s | -26 % | -5 % | | Sep 30 | 701 TH/s | -37 % | -20 % | | Oct 4 | 651 TH/s | -42 % | -25 % | This scenario gives us less space to achieve TTD before Devcon. But we have more time to adjust TTD based on a potential DAG hashrate drop. Here are other TTD values considering the lower hashrate: | TTD | Expected date | Hashrate at Bellatrix | Drop by The Merge | Drop by Sep 30 | | ----------------------- | ------------- | --------------------- | ----------------- | -------------- | | 58980000000000000000000 | September 18 | 1241 TH/s | 5% | 23% | | 58800000000000000000000 | September 15 | 1168 TH/s | 10% | 27% | | 58480000000000000000000 | September 11 | 1039 TH/s | 20% | 35% |