This is a bit misleading as the savings calculator is just showing you the future value of the payments. What Warden needs is to calculate the present value because in theory the 240k can also be invested today and grow and it grows at a faster rate than your payments because it's a lump sum at the start of the period rather than smaller sums over the course of 35 years.
There would be two ways to calculate this. First, if you assume the payments will occur in perpetuity then you need a present value of a perpetuity calculator. I probably wouldn't assume that though because the placement of the cell tower can change by the time the lease is over and **** in 44 years there may not even be cell towers as some new technology will render it obsolete. Not to mention Warden could simply never see the bulk of those payments because something may happen that results in him having to sell his property.
So I would just use the present value calculate in Microsoft Excel. The next question is what rate to input and that depends on what rate Warden thinks he can invest at. The higher the rate, the lower the value in present value terms. If we assume a 5% rate if he simply invested in stocks or something then you would enter 5%/12 as the rate as the payments are monthly, 420 and payment periods (35 years left * 12 months), and a payment of 1,200 a month. You would put in 0 for future value as you don't get lump sum payment at the end. You would then input 1 or 0 depending on whether the payment is at the beginning or end of the month.
That would work out to a present value of around 237-238k depending on whether you did the payments at beginning or end which is pretty consistent with the 240k they are offering.
So I suspect they just did a basic PV formula assuming a basic rate of return around 5% to come up with the lump sum value. So it's a fair deal unless Warden things he can get a higher rate of return. If for example he invests in stocks or mutual funds, returns over that time period are generally higher and it would be a bad deal for him. If you assumed a 10% rate of return then the PV drops to 139k or so.
Personally I would take the lump sum because my returns by just investing in stocks and bonds have been between 15 or 20% which means it's better for me to take the 240k and invest in the stock market now at 15 or 20%.
The only other thing to consider is as Ommy notes, the tax rates would be different as you tax rate may be lower in the future but that is assuming taxes remain the way they are now. For all we know the tax rates could go up or retirement ages could be extended so the issue here is you are gambling on a future 35 years away that could be very different than the reality today. Not to mention, Warden's not going to hit retirement until late in the lease so the reality is most of the payments will be made while he is still working and while if he is progressing at his job, his tax rate may be increasing. However, the biggest issue is that Warden's dad is 77 so already retired. So I would take the money now and lock in his father's presumably low tax rate now with a known tax rate rather than gamble that in the future Warden's tax rate will be lower than his dad's.
So unless Warden can only get a return less than 5% or unless he has confidence in the fact the company will extend the lease beyond the current 44 year lease or he has a favorable view of what will happen with respect to taxes and retirement, it's really a gamble not worth taking IMO. Having said that, I would still negotiation for more money as the property isn't going anywhere so if their offer 240k to start then they may be willing to go higher.
Edit - I did do a bit of a fudge in that I didn't take into account the 3% rate because it's just inflation. If you really wanted to take that into account, you would need to use the NPV function in excel but I didn't **** with that because it requires you to put in each pay period separately since the payment is changing and I had no desire to input 420 separate payments. In the end, I don't think it changes the real value of money because again it's just inflation.
